src/liballoc/collections/binary_heap.rs

   1 //! A priority queue implemented with a binary heap.
   2 //!
   3 //! Insertion and popping the largest element have `O(log n)` time complexity.
   4 //! Checking the largest element is `O(1)`. Converting a vector to a binary heap
   5 //! can be done in-place, and has `O(n)` complexity. A binary heap can also be
   6 //! converted to a sorted vector in-place, allowing it to be used for an `O(n
   7 //! log n)` in-place heapsort.
   8 //!
   9 //! # Examples
  10 //!
  11 //! This is a larger example that implements [Dijkstra's algorithm][dijkstra]
  12 //! to solve the [shortest path problem][sssp] on a [directed graph][dir_graph].
  13 //! It shows how to use [`BinaryHeap`] with custom types.
  14 //!
  15 //! [dijkstra]: http://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
  16 //! [sssp]: http://en.wikipedia.org/wiki/Shortest_path_problem
  17 //! [dir_graph]: http://en.wikipedia.org/wiki/Directed_graph
  18 //! [`BinaryHeap`]: struct.BinaryHeap.html
  19 //!
  20 //! ```
  21 //! use std::cmp::Ordering;
  22 //! use std::collections::BinaryHeap;
  23 //! use std::usize;
  24 //!
  25 //! #[derive(Copy, Clone, Eq, PartialEq)]
  26 //! struct State {
  27 //!     cost: usize,
  28 //!     position: usize,
  29 //! }
  30 //!
  31 //! // The priority queue depends on `Ord`.
  32 //! // Explicitly implement the trait so the queue becomes a min-heap
  33 //! // instead of a max-heap.
  34 //! impl Ord for State {
  35 //!     fn cmp(&self, other: &State) -> Ordering {
  36 //!         // Notice that the we flip the ordering on costs.
  37 //!         // In case of a tie we compare positions - this step is necessary
  38 //!         // to make implementations of `PartialEq` and `Ord` consistent.
  39 //!         other.cost.cmp(&self.cost)
  40 //!             .then_with(|| self.position.cmp(&other.position))
  41 //!     }
  42 //! }
  43 //!
  44 //! // `PartialOrd` needs to be implemented as well.
  45 //! impl PartialOrd for State {
  46 //!     fn partial_cmp(&self, other: &State) -> Option<Ordering> {
  47 //!         Some(self.cmp(other))
  48 //!     }
  49 //! }
  50 //!
  51 //! // Each node is represented as an `usize`, for a shorter implementation.
  52 //! struct Edge {
  53 //!     node: usize,
  54 //!     cost: usize,
  55 //! }
  56 //!
  57 //! // Dijkstra's shortest path algorithm.
  58 //!
  59 //! // Start at `start` and use `dist` to track the current shortest distance
  60 //! // to each node. This implementation isn't memory-efficient as it may leave duplicate
  61 //! // nodes in the queue. It also uses `usize::MAX` as a sentinel value,
  62 //! // for a simpler implementation.
  63 //! fn shortest_path(adj_list: &Vec<Vec<Edge>>, start: usize, goal: usize) -> Option<usize> {
  64 //!     // dist[node] = current shortest distance from `start` to `node`
  65 //!     let mut dist: Vec<_> = (0..adj_list.len()).map(|_| usize::MAX).collect();
  66 //!
  67 //!     let mut heap = BinaryHeap::new();
  68 //!
  69 //!     // We're at `start`, with a zero cost
  70 //!     dist[start] = 0;
  71 //!     heap.push(State { cost: 0, position: start });
  72 //!
  73 //!     // Examine the frontier with lower cost nodes first (min-heap)
  74 //!     while let Some(State { cost, position }) = heap.pop() {
  75 //!         // Alternatively we could have continued to find all shortest paths
  76 //!         if position == goal { return Some(cost); }
  77 //!
  78 //!         // Important as we may have already found a better way
  79 //!         if cost > dist[position] { continue; }
  80 //!
  81 //!         // For each node we can reach, see if we can find a way with
  82 //!         // a lower cost going through this node
  83 //!         for edge in &adj_list[position] {
  84 //!             let next = State { cost: cost + edge.cost, position: edge.node };
  85 //!
  86 //!             // If so, add it to the frontier and continue
  87 //!             if next.cost < dist[next.position] {
  88 //!                 heap.push(next);
  89 //!                 // Relaxation, we have now found a better way
  90 //!                 dist[next.position] = next.cost;
  91 //!             }
  92 //!         }
  93 //!     }
  94 //!
  95 //!     // Goal not reachable
  96 //!     None
  97 //! }
  98 //!
  99 //! fn main() {
 100 //!     // This is the directed graph we're going to use.
 101 //!     // The node numbers correspond to the different states,
 102 //!     // and the edge weights symbolize the cost of moving
 103 //!     // from one node to another.
 104 //!     // Note that the edges are one-way.
 105 //!     //
 106 //!     //                  7
 107 //!     //          +-----------------+
 108 //!     //          |                 |
 109 //!     //          v   1        2    |  2
 110 //!     //          0 -----> 1 -----> 3 ---> 4
 111 //!     //          |        ^        ^      ^
 112 //!     //          |        | 1      |      |
 113 //!     //          |        |        | 3    | 1
 114 //!     //          +------> 2 -------+      |
 115 //!     //           10      |               |
 116 //!     //                   +---------------+
 117 //!     //
 118 //!     // The graph is represented as an adjacency list where each index,
 119 //!     // corresponding to a node value, has a list of outgoing edges.
 120 //!     // Chosen for its efficiency.
 121 //!     let graph = vec![
 122 //!         // Node 0
 123 //!         vec![Edge { node: 2, cost: 10 },
 124 //!              Edge { node: 1, cost: 1 }],
 125 //!         // Node 1
 126 //!         vec![Edge { node: 3, cost: 2 }],
 127 //!         // Node 2
 128 //!         vec![Edge { node: 1, cost: 1 },
 129 //!              Edge { node: 3, cost: 3 },
 130 //!              Edge { node: 4, cost: 1 }],
 131 //!         // Node 3
 132 //!         vec![Edge { node: 0, cost: 7 },
 133 //!              Edge { node: 4, cost: 2 }],
 134 //!         // Node 4
 135 //!         vec![]];
 136 //!
 137 //!     assert_eq!(shortest_path(&graph, 0, 1), Some(1));
 138 //!     assert_eq!(shortest_path(&graph, 0, 3), Some(3));
 139 //!     assert_eq!(shortest_path(&graph, 3, 0), Some(7));
 140 //!     assert_eq!(shortest_path(&graph, 0, 4), Some(5));
 141 //!     assert_eq!(shortest_path(&graph, 4, 0), None);
 142 //! }
 143 //! ```
 144
 145 #![allow(missing_docs)]
 146 #![stable(feature = "rust1", since = "1.0.0")]
 147
 148 use core::ops::{Deref, DerefMut};
 149 use core::iter::{FromIterator, FusedIterator};
 150 use core::mem::{swap, size_of, ManuallyDrop};
 151 use core::ptr;
 152 use core::fmt;
 153
 154 use crate::slice;
 155 use crate::vec::{self, Vec};
 156
 157 use super::SpecExtend;
 158
 159 /// A priority queue implemented with a binary heap.
 160 ///
 161 /// This will be a max-heap.
 162 ///
 163 /// It is a logic error for an item to be modified in such a way that the
 164 /// item's ordering relative to any other item, as determined by the `Ord`
 165 /// trait, changes while it is in the heap. This is normally only possible
 166 /// through `Cell`, `RefCell`, global state, I/O, or unsafe code.
 167 ///
 168 /// # Examples
 169 ///
 170 /// ```
 171 /// use std::collections::BinaryHeap;
 172 ///
 173 /// // Type inference lets us omit an explicit type signature (which
 174 /// // would be `BinaryHeap<i32>` in this example).
 175 /// let mut heap = BinaryHeap::new();
 176 ///
 177 /// // We can use peek to look at the next item in the heap. In this case,
 178 /// // there's no items in there yet so we get None.
 179 /// assert_eq!(heap.peek(), None);
 180 ///
 181 /// // Let's add some scores...
 182 /// heap.push(1);
 183 /// heap.push(5);
 184 /// heap.push(2);
 185 ///
 186 /// // Now peek shows the most important item in the heap.
 187 /// assert_eq!(heap.peek(), Some(&5));
 188 ///
 189 /// // We can check the length of a heap.
 190 /// assert_eq!(heap.len(), 3);
 191 ///
 192 /// // We can iterate over the items in the heap, although they are returned in
 193 /// // a random order.
 194 /// for x in &heap {
 195 ///     println!("{}", x);
 196 /// }
 197 ///
 198 /// // If we instead pop these scores, they should come back in order.
 199 /// assert_eq!(heap.pop(), Some(5));
 200 /// assert_eq!(heap.pop(), Some(2));
 201 /// assert_eq!(heap.pop(), Some(1));
 202 /// assert_eq!(heap.pop(), None);
 203 ///
 204 /// // We can clear the heap of any remaining items.
 205 /// heap.clear();
 206 ///
 207 /// // The heap should now be empty.
 208 /// assert!(heap.is_empty())
 209 /// ```
 210 #[stable(feature = "rust1", since = "1.0.0")]
 211 pub struct BinaryHeap<T> {
 212     data: Vec<T>,
 213 }
 214
 215 /// Structure wrapping a mutable reference to the greatest item on a
 216 /// `BinaryHeap`.
 217 ///
 218 /// This `struct` is created by the [`peek_mut`] method on [`BinaryHeap`]. See
 219 /// its documentation for more.
 220 ///
 221 /// [`peek_mut`]: struct.BinaryHeap.html#method.peek_mut
 222 /// [`BinaryHeap`]: struct.BinaryHeap.html
 223 #[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
 224 pub struct PeekMut<'a, T: 'a + Ord> {
 225     heap: &'a mut BinaryHeap<T>,
 226     sift: bool,
 227 }
 228
 229 #[stable(feature = "collection_debug", since = "1.17.0")]
 230 impl<T: Ord + fmt::Debug> fmt::Debug for PeekMut<'_, T> {
 231     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 232         f.debug_tuple("PeekMut")
 233          .field(&self.heap.data[0])
 234          .finish()
 235     }
 236 }
 237
 238 #[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
 239 impl<T: Ord> Drop for PeekMut<'_, T> {
 240     fn drop(&mut self) {
 241         if self.sift {
 242             self.heap.sift_down(0);
 243         }
 244     }
 245 }
 246
 247 #[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
 248 impl<T: Ord> Deref for PeekMut<'_, T> {
 249     type Target = T;
 250     fn deref(&self) -> &T {
 251         debug_assert!(!self.heap.is_empty());
 252         // SAFE: PeekMut is only instantiated for non-empty heaps
 253         unsafe { self.heap.data.get_unchecked(0) }
 254     }
 255 }
 256
 257 #[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
 258 impl<T: Ord> DerefMut for PeekMut<'_, T> {
 259     fn deref_mut(&mut self) -> &mut T {
 260         debug_assert!(!self.heap.is_empty());
 261         // SAFE: PeekMut is only instantiated for non-empty heaps
 262         unsafe { self.heap.data.get_unchecked_mut(0) }
 263     }
 264 }
 265
 266 impl<'a, T: Ord> PeekMut<'a, T> {
 267     /// Removes the peeked value from the heap and returns it.
 268     #[stable(feature = "binary_heap_peek_mut_pop", since = "1.18.0")]
 269     pub fn pop(mut this: PeekMut<'a, T>) -> T {
 270         let value = this.heap.pop().unwrap();
 271         this.sift = false;
 272         value
 273     }
 274 }
 275
 276 #[stable(feature = "rust1", since = "1.0.0")]
 277 impl<T: Clone> Clone for BinaryHeap<T> {
 278     fn clone(&self) -> Self {
 279         BinaryHeap { data: self.data.clone() }
 280     }
 281
 282     fn clone_from(&mut self, source: &Self) {
 283         self.data.clone_from(&source.data);
 284     }
 285 }
 286
 287 #[stable(feature = "rust1", since = "1.0.0")]
 288 impl<T: Ord> Default for BinaryHeap<T> {
 289     /// Creates an empty `BinaryHeap<T>`.
 290     #[inline]
 291     fn default() -> BinaryHeap<T> {
 292         BinaryHeap::new()
 293     }
 294 }
 295
 296 #[stable(feature = "binaryheap_debug", since = "1.4.0")]
 297 impl<T: fmt::Debug> fmt::Debug for BinaryHeap<T> {
 298     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 299         f.debug_list().entries(self.iter()).finish()
 300     }
 301 }
 302
 303 impl<T: Ord> BinaryHeap<T> {
 304     /// Creates an empty `BinaryHeap` as a max-heap.
 305     ///
 306     /// # Examples
 307     ///
 308     /// Basic usage:
 309     ///
 310     /// ```
 311     /// use std::collections::BinaryHeap;
 312     /// let mut heap = BinaryHeap::new();
 313     /// heap.push(4);
 314     /// ```
 315     #[stable(feature = "rust1", since = "1.0.0")]
 316     pub fn new() -> BinaryHeap<T> {
 317         BinaryHeap { data: vec![] }
 318     }
 319
 320     /// Creates an empty `BinaryHeap` with a specific capacity.
 321     /// This preallocates enough memory for `capacity` elements,
 322     /// so that the `BinaryHeap` does not have to be reallocated
 323     /// until it contains at least that many values.
 324     ///
 325     /// # Examples
 326     ///
 327     /// Basic usage:
 328     ///
 329     /// ```
 330     /// use std::collections::BinaryHeap;
 331     /// let mut heap = BinaryHeap::with_capacity(10);
 332     /// heap.push(4);
 333     /// ```
 334     #[stable(feature = "rust1", since = "1.0.0")]
 335     pub fn with_capacity(capacity: usize) -> BinaryHeap<T> {
 336         BinaryHeap { data: Vec::with_capacity(capacity) }
 337     }
 338
 339     /// Returns a mutable reference to the greatest item in the binary heap, or
 340     /// `None` if it is empty.
 341     ///
 342     /// Note: If the `PeekMut` value is leaked, the heap may be in an
 343     /// inconsistent state.
 344     ///
 345     /// # Examples
 346     ///
 347     /// Basic usage:
 348     ///
 349     /// ```
 350     /// use std::collections::BinaryHeap;
 351     /// let mut heap = BinaryHeap::new();
 352     /// assert!(heap.peek_mut().is_none());
 353     ///
 354     /// heap.push(1);
 355     /// heap.push(5);
 356     /// heap.push(2);
 357     /// {
 358     ///     let mut val = heap.peek_mut().unwrap();
 359     ///     *val = 0;
 360     /// }
 361     /// assert_eq!(heap.peek(), Some(&2));
 362     /// ```
 363     #[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
 364     pub fn peek_mut(&mut self) -> Option<PeekMut<'_, T>> {
 365         if self.is_empty() {
 366             None
 367         } else {
 368             Some(PeekMut {
 369                 heap: self,
 370                 sift: true,
 371             })
 372         }
 373     }
 374
 375     /// Removes the greatest item from the binary heap and returns it, or `None` if it
 376     /// is empty.
 377     ///
 378     /// # Examples
 379     ///
 380     /// Basic usage:
 381     ///
 382     /// ```
 383     /// use std::collections::BinaryHeap;
 384     /// let mut heap = BinaryHeap::from(vec![1, 3]);
 385     ///
 386     /// assert_eq!(heap.pop(), Some(3));
 387     /// assert_eq!(heap.pop(), Some(1));
 388     /// assert_eq!(heap.pop(), None);
 389     /// ```
 390     #[stable(feature = "rust1", since = "1.0.0")]
 391     pub fn pop(&mut self) -> Option<T> {
 392         self.data.pop().map(|mut item| {
 393             if !self.is_empty() {
 394                 swap(&mut item, &mut self.data[0]);
 395                 self.sift_down_to_bottom(0);
 396             }
 397             item
 398         })
 399     }
 400
 401     /// Pushes an item onto the binary heap.
 402     ///
 403     /// # Examples
 404     ///
 405     /// Basic usage:
 406     ///
 407     /// ```
 408     /// use std::collections::BinaryHeap;
 409     /// let mut heap = BinaryHeap::new();
 410     /// heap.push(3);
 411     /// heap.push(5);
 412     /// heap.push(1);
 413     ///
 414     /// assert_eq!(heap.len(), 3);
 415     /// assert_eq!(heap.peek(), Some(&5));
 416     /// ```
 417     #[stable(feature = "rust1", since = "1.0.0")]
 418     pub fn push(&mut self, item: T) {
 419         let old_len = self.len();
 420         self.data.push(item);
 421         self.sift_up(0, old_len);
 422     }
 423
 424     /// Consumes the `BinaryHeap` and returns a vector in sorted
 425     /// (ascending) order.
 426     ///
 427     /// # Examples
 428     ///
 429     /// Basic usage:
 430     ///
 431     /// ```
 432     /// use std::collections::BinaryHeap;
 433     ///
 434     /// let mut heap = BinaryHeap::from(vec![1, 2, 4, 5, 7]);
 435     /// heap.push(6);
 436     /// heap.push(3);
 437     ///
 438     /// let vec = heap.into_sorted_vec();
 439     /// assert_eq!(vec, [1, 2, 3, 4, 5, 6, 7]);
 440     /// ```
 441     #[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
 442     pub fn into_sorted_vec(mut self) -> Vec<T> {
 443         let mut end = self.len();
 444         while end > 1 {
 445             end -= 1;
 446             self.data.swap(0, end);
 447             self.sift_down_range(0, end);
 448         }
 449         self.into_vec()
 450     }
 451
 452     // The implementations of sift_up and sift_down use unsafe blocks in
 453     // order to move an element out of the vector (leaving behind a
 454     // hole), shift along the others and move the removed element back into the
 455     // vector at the final location of the hole.
 456     // The `Hole` type is used to represent this, and make sure
 457     // the hole is filled back at the end of its scope, even on panic.
 458     // Using a hole reduces the constant factor compared to using swaps,
 459     // which involves twice as many moves.
 460     fn sift_up(&mut self, start: usize, pos: usize) -> usize {
 461         unsafe {
 462             // Take out the value at `pos` and create a hole.
 463             let mut hole = Hole::new(&mut self.data, pos);
 464
 465             while hole.pos() > start {
 466                 let parent = (hole.pos() - 1) / 2;
 467                 if hole.element() <= hole.get(parent) {
 468                     break;
 469                 }
 470                 hole.move_to(parent);
 471             }
 472             hole.pos()
 473         }
 474     }
 475
 476     /// Take an element at `pos` and move it down the heap,
 477     /// while its children are larger.
 478     fn sift_down_range(&mut self, pos: usize, end: usize) {
 479         unsafe {
 480             let mut hole = Hole::new(&mut self.data, pos);
 481             let mut child = 2 * pos + 1;
 482             while child < end {
 483                 let right = child + 1;
 484                 // compare with the greater of the two children
 485                 if right < end && !(hole.get(child) > hole.get(right)) {
 486                     child = right;
 487                 }
 488                 // if we are already in order, stop.
 489                 if hole.element() >= hole.get(child) {
 490                     break;
 491                 }
 492                 hole.move_to(child);
 493                 child = 2 * hole.pos() + 1;
 494             }
 495         }
 496     }
 497
 498     fn sift_down(&mut self, pos: usize) {
 499         let len = self.len();
 500         self.sift_down_range(pos, len);
 501     }
 502
 503     /// Take an element at `pos` and move it all the way down the heap,
 504     /// then sift it up to its position.
 505     ///
 506     /// Note: This is faster when the element is known to be large / should
 507     /// be closer to the bottom.
 508     fn sift_down_to_bottom(&mut self, mut pos: usize) {
 509         let end = self.len();
 510         let start = pos;
 511         unsafe {
 512             let mut hole = Hole::new(&mut self.data, pos);
 513             let mut child = 2 * pos + 1;
 514             while child < end {
 515                 let right = child + 1;
 516                 // compare with the greater of the two children
 517                 if right < end && !(hole.get(child) > hole.get(right)) {
 518                     child = right;
 519                 }
 520                 hole.move_to(child);
 521                 child = 2 * hole.pos() + 1;
 522             }
 523             pos = hole.pos;
 524         }
 525         self.sift_up(start, pos);
 526     }
 527
 528     fn rebuild(&mut self) {
 529         let mut n = self.len() / 2;
 530         while n > 0 {
 531             n -= 1;
 532             self.sift_down(n);
 533         }
 534     }
 535
 536     /// Moves all the elements of `other` into `self`, leaving `other` empty.
 537     ///
 538     /// # Examples
 539     ///
 540     /// Basic usage:
 541     ///
 542     /// ```
 543     /// use std::collections::BinaryHeap;
 544     ///
 545     /// let v = vec![-10, 1, 2, 3, 3];
 546     /// let mut a = BinaryHeap::from(v);
 547     ///
 548     /// let v = vec![-20, 5, 43];
 549     /// let mut b = BinaryHeap::from(v);
 550     ///
 551     /// a.append(&mut b);
 552     ///
 553     /// assert_eq!(a.into_sorted_vec(), [-20, -10, 1, 2, 3, 3, 5, 43]);
 554     /// assert!(b.is_empty());
 555     /// ```
 556     #[stable(feature = "binary_heap_append", since = "1.11.0")]
 557     pub fn append(&mut self, other: &mut Self) {
 558         if self.len() < other.len() {
 559             swap(self, other);
 560         }
 561
 562         if other.is_empty() {
 563             return;
 564         }
 565
 566         #[inline(always)]
 567         fn log2_fast(x: usize) -> usize {
 568             8 * size_of::<usize>() - (x.leading_zeros() as usize) - 1
 569         }
 570
 571         // `rebuild` takes O(len1 + len2) operations
 572         // and about 2 * (len1 + len2) comparisons in the worst case
 573         // while `extend` takes O(len2 * log_2(len1)) operations
 574         // and about 1 * len2 * log_2(len1) comparisons in the worst case,
 575         // assuming len1 >= len2.
 576         #[inline]
 577         fn better_to_rebuild(len1: usize, len2: usize) -> bool {
 578             2 * (len1 + len2) < len2 * log2_fast(len1)
 579         }
 580
 581         if better_to_rebuild(self.len(), other.len()) {
 582             self.data.append(&mut other.data);
 583             self.rebuild();
 584         } else {
 585             self.extend(other.drain());
 586         }
 587     }
 588 }
 589
 590 impl<T> BinaryHeap<T> {
 591     /// Returns an iterator visiting all values in the underlying vector, in
 592     /// arbitrary order.
 593     ///
 594     /// # Examples
 595     ///
 596     /// Basic usage:
 597     ///
 598     /// ```
 599     /// use std::collections::BinaryHeap;
 600     /// let heap = BinaryHeap::from(vec![1, 2, 3, 4]);
 601     ///
 602     /// // Print 1, 2, 3, 4 in arbitrary order
 603     /// for x in heap.iter() {
 604     ///     println!("{}", x);
 605     /// }
 606     /// ```
 607     #[stable(feature = "rust1", since = "1.0.0")]
 608     pub fn iter(&self) -> Iter<'_, T> {
 609         Iter { iter: self.data.iter() }
 610     }
 611
 612     /// Returns the greatest item in the binary heap, or `None` if it is empty.
 613     ///
 614     /// # Examples
 615     ///
 616     /// Basic usage:
 617     ///
 618     /// ```
 619     /// use std::collections::BinaryHeap;
 620     /// let mut heap = BinaryHeap::new();
 621     /// assert_eq!(heap.peek(), None);
 622     ///
 623     /// heap.push(1);
 624     /// heap.push(5);
 625     /// heap.push(2);
 626     /// assert_eq!(heap.peek(), Some(&5));
 627     ///
 628     /// ```
 629     #[stable(feature = "rust1", since = "1.0.0")]
 630     pub fn peek(&self) -> Option<&T> {
 631         self.data.get(0)
 632     }
 633
 634     /// Returns the number of elements the binary heap can hold without reallocating.
 635     ///
 636     /// # Examples
 637     ///
 638     /// Basic usage:
 639     ///
 640     /// ```
 641     /// use std::collections::BinaryHeap;
 642     /// let mut heap = BinaryHeap::with_capacity(100);
 643     /// assert!(heap.capacity() >= 100);
 644     /// heap.push(4);
 645     /// ```
 646     #[stable(feature = "rust1", since = "1.0.0")]
 647     pub fn capacity(&self) -> usize {
 648         self.data.capacity()
 649     }
 650
 651     /// Reserves the minimum capacity for exactly `additional` more elements to be inserted in the
 652     /// given `BinaryHeap`. Does nothing if the capacity is already sufficient.
 653     ///
 654     /// Note that the allocator may give the collection more space than it requests. Therefore
 655     /// capacity can not be relied upon to be precisely minimal. Prefer [`reserve`] if future
 656     /// insertions are expected.
 657     ///
 658     /// # Panics
 659     ///
 660     /// Panics if the new capacity overflows `usize`.
 661     ///
 662     /// # Examples
 663     ///
 664     /// Basic usage:
 665     ///
 666     /// ```
 667     /// use std::collections::BinaryHeap;
 668     /// let mut heap = BinaryHeap::new();
 669     /// heap.reserve_exact(100);
 670     /// assert!(heap.capacity() >= 100);
 671     /// heap.push(4);
 672     /// ```
 673     ///
 674     /// [`reserve`]: #method.reserve
 675     #[stable(feature = "rust1", since = "1.0.0")]
 676     pub fn reserve_exact(&mut self, additional: usize) {
 677         self.data.reserve_exact(additional);
 678     }
 679
 680     /// Reserves capacity for at least `additional` more elements to be inserted in the
 681     /// `BinaryHeap`. The collection may reserve more space to avoid frequent reallocations.
 682     ///
 683     /// # Panics
 684     ///
 685     /// Panics if the new capacity overflows `usize`.
 686     ///
 687     /// # Examples
 688     ///
 689     /// Basic usage:
 690     ///
 691     /// ```
 692     /// use std::collections::BinaryHeap;
 693     /// let mut heap = BinaryHeap::new();
 694     /// heap.reserve(100);
 695     /// assert!(heap.capacity() >= 100);
 696     /// heap.push(4);
 697     /// ```
 698     #[stable(feature = "rust1", since = "1.0.0")]
 699     pub fn reserve(&mut self, additional: usize) {
 700         self.data.reserve(additional);
 701     }
 702
 703     /// Discards as much additional capacity as possible.
 704     ///
 705     /// # Examples
 706     ///
 707     /// Basic usage:
 708     ///
 709     /// ```
 710     /// use std::collections::BinaryHeap;
 711     /// let mut heap: BinaryHeap<i32> = BinaryHeap::with_capacity(100);
 712     ///
 713     /// assert!(heap.capacity() >= 100);
 714     /// heap.shrink_to_fit();
 715     /// assert!(heap.capacity() == 0);
 716     /// ```
 717     #[stable(feature = "rust1", since = "1.0.0")]
 718     pub fn shrink_to_fit(&mut self) {
 719         self.data.shrink_to_fit();
 720     }
 721
 722     /// Discards capacity with a lower bound.
 723     ///
 724     /// The capacity will remain at least as large as both the length
 725     /// and the supplied value.
 726     ///
 727     /// Panics if the current capacity is smaller than the supplied
 728     /// minimum capacity.
 729     ///
 730     /// # Examples
 731     ///
 732     /// ```
 733     /// #![feature(shrink_to)]
 734     /// use std::collections::BinaryHeap;
 735     /// let mut heap: BinaryHeap<i32> = BinaryHeap::with_capacity(100);
 736     ///
 737     /// assert!(heap.capacity() >= 100);
 738     /// heap.shrink_to(10);
 739     /// assert!(heap.capacity() >= 10);
 740     /// ```
 741     #[inline]
 742     #[unstable(feature = "shrink_to", reason = "new API", issue="56431")]
 743     pub fn shrink_to(&mut self, min_capacity: usize) {
 744         self.data.shrink_to(min_capacity)
 745     }
 746
 747     /// Consumes the `BinaryHeap` and returns the underlying vector
 748     /// in arbitrary order.
 749     ///
 750     /// # Examples
 751     ///
 752     /// Basic usage:
 753     ///
 754     /// ```
 755     /// use std::collections::BinaryHeap;
 756     /// let heap = BinaryHeap::from(vec![1, 2, 3, 4, 5, 6, 7]);
 757     /// let vec = heap.into_vec();
 758     ///
 759     /// // Will print in some order
 760     /// for x in vec {
 761     ///     println!("{}", x);
 762     /// }
 763     /// ```
 764     #[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
 765     pub fn into_vec(self) -> Vec<T> {
 766         self.into()
 767     }
 768
 769     /// Returns the length of the binary heap.
 770     ///
 771     /// # Examples
 772     ///
 773     /// Basic usage:
 774     ///
 775     /// ```
 776     /// use std::collections::BinaryHeap;
 777     /// let heap = BinaryHeap::from(vec![1, 3]);
 778     ///
 779     /// assert_eq!(heap.len(), 2);
 780     /// ```
 781     #[stable(feature = "rust1", since = "1.0.0")]
 782     pub fn len(&self) -> usize {
 783         self.data.len()
 784     }
 785
 786     /// Checks if the binary heap is empty.
 787     ///
 788     /// # Examples
 789     ///
 790     /// Basic usage:
 791     ///
 792     /// ```
 793     /// use std::collections::BinaryHeap;
 794     /// let mut heap = BinaryHeap::new();
 795     ///
 796     /// assert!(heap.is_empty());
 797     ///
 798     /// heap.push(3);
 799     /// heap.push(5);
 800     /// heap.push(1);
 801     ///
 802     /// assert!(!heap.is_empty());
 803     /// ```
 804     #[stable(feature = "rust1", since = "1.0.0")]
 805     pub fn is_empty(&self) -> bool {
 806         self.len() == 0
 807     }
 808
 809     /// Clears the binary heap, returning an iterator over the removed elements.
 810     ///
 811     /// The elements are removed in arbitrary order.
 812     ///
 813     /// # Examples
 814     ///
 815     /// Basic usage:
 816     ///
 817     /// ```
 818     /// use std::collections::BinaryHeap;
 819     /// let mut heap = BinaryHeap::from(vec![1, 3]);
 820     ///
 821     /// assert!(!heap.is_empty());
 822     ///
 823     /// for x in heap.drain() {
 824     ///     println!("{}", x);
 825     /// }
 826     ///
 827     /// assert!(heap.is_empty());
 828     /// ```
 829     #[inline]
 830     #[stable(feature = "drain", since = "1.6.0")]
 831     pub fn drain(&mut self) -> Drain<'_, T> {
 832         Drain { iter: self.data.drain(..) }
 833     }
 834
 835     /// Drops all items from the binary heap.
 836     ///
 837     /// # Examples
 838     ///
 839     /// Basic usage:
 840     ///
 841     /// ```
 842     /// use std::collections::BinaryHeap;
 843     /// let mut heap = BinaryHeap::from(vec![1, 3]);
 844     ///
 845     /// assert!(!heap.is_empty());
 846     ///
 847     /// heap.clear();
 848     ///
 849     /// assert!(heap.is_empty());
 850     /// ```
 851     #[stable(feature = "rust1", since = "1.0.0")]
 852     pub fn clear(&mut self) {
 853         self.drain();
 854     }
 855 }
 856
 857 /// Hole represents a hole in a slice i.e., an index without valid value
 858 /// (because it was moved from or duplicated).
 859 /// In drop, `Hole` will restore the slice by filling the hole
 860 /// position with the value that was originally removed.
 861 struct Hole<'a, T: 'a> {
 862     data: &'a mut [T],
 863     elt: ManuallyDrop<T>,
 864     pos: usize,
 865 }
 866
 867 impl<'a, T> Hole<'a, T> {
 868     /// Create a new `Hole` at index `pos`.
 869     ///
 870     /// Unsafe because pos must be within the data slice.
 871     #[inline]
 872     unsafe fn new(data: &'a mut [T], pos: usize) -> Self {
 873         debug_assert!(pos < data.len());
 874         // SAFE: pos should be inside the slice
 875         let elt = ptr::read(data.get_unchecked(pos));
 876         Hole {
 877             data,
 878             elt: ManuallyDrop::new(elt),
 879             pos,
 880         }
 881     }
 882
 883     #[inline]
 884     fn pos(&self) -> usize {
 885         self.pos
 886     }
 887
 888     /// Returns a reference to the element removed.
 889     #[inline]
 890     fn element(&self) -> &T {
 891         &self.elt
 892     }
 893
 894     /// Returns a reference to the element at `index`.
 895     ///
 896     /// Unsafe because index must be within the data slice and not equal to pos.
 897     #[inline]
 898     unsafe fn get(&self, index: usize) -> &T {
 899         debug_assert!(index != self.pos);
 900         debug_assert!(index < self.data.len());
 901         self.data.get_unchecked(index)
 902     }
 903
 904     /// Move hole to new location
 905     ///
 906     /// Unsafe because index must be within the data slice and not equal to pos.
 907     #[inline]
 908     unsafe fn move_to(&mut self, index: usize) {
 909         debug_assert!(index != self.pos);
 910         debug_assert!(index < self.data.len());
 911         let index_ptr: *const _ = self.data.get_unchecked(index);
 912         let hole_ptr = self.data.get_unchecked_mut(self.pos);
 913         ptr::copy_nonoverlapping(index_ptr, hole_ptr, 1);
 914         self.pos = index;
 915     }
 916 }
 917
 918 impl<T> Drop for Hole<'_, T> {
 919     #[inline]
 920     fn drop(&mut self) {
 921         // fill the hole again
 922         unsafe {
 923             let pos = self.pos;
 924             ptr::copy_nonoverlapping(&*self.elt, self.data.get_unchecked_mut(pos), 1);
 925         }
 926     }
 927 }
 928
 929 /// An iterator over the elements of a `BinaryHeap`.
 930 ///
 931 /// This `struct` is created by the [`iter`] method on [`BinaryHeap`]. See its
 932 /// documentation for more.
 933 ///
 934 /// [`iter`]: struct.BinaryHeap.html#method.iter
 935 /// [`BinaryHeap`]: struct.BinaryHeap.html
 936 #[stable(feature = "rust1", since = "1.0.0")]
 937 pub struct Iter<'a, T: 'a> {
 938     iter: slice::Iter<'a, T>,
 939 }
 940
 941 #[stable(feature = "collection_debug", since = "1.17.0")]
 942 impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
 943     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 944         f.debug_tuple("Iter")
 945          .field(&self.iter.as_slice())
 946          .finish()
 947     }
 948 }
 949
 950 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
 951 #[stable(feature = "rust1", since = "1.0.0")]
 952 impl<T> Clone for Iter<'_, T> {
 953     fn clone(&self) -> Self {
 954         Iter { iter: self.iter.clone() }
 955     }
 956 }
 957
 958 #[stable(feature = "rust1", since = "1.0.0")]
 959 impl<'a, T> Iterator for Iter<'a, T> {
 960     type Item = &'a T;
 961
 962     #[inline]
 963     fn next(&mut self) -> Option<&'a T> {
 964         self.iter.next()
 965     }
 966
 967     #[inline]
 968     fn size_hint(&self) -> (usize, Option<usize>) {
 969         self.iter.size_hint()
 970     }
 971 }
 972
 973 #[stable(feature = "rust1", since = "1.0.0")]
 974 impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
 975     #[inline]
 976     fn next_back(&mut self) -> Option<&'a T> {
 977         self.iter.next_back()
 978     }
 979 }
 980
 981 #[stable(feature = "rust1", since = "1.0.0")]
 982 impl<T> ExactSizeIterator for Iter<'_, T> {
 983     fn is_empty(&self) -> bool {
 984         self.iter.is_empty()
 985     }
 986 }
 987
 988 #[stable(feature = "fused", since = "1.26.0")]
 989 impl<T> FusedIterator for Iter<'_, T> {}
 990
 991 /// An owning iterator over the elements of a `BinaryHeap`.
 992 ///
 993 /// This `struct` is created by the [`into_iter`] method on [`BinaryHeap`][`BinaryHeap`]
 994 /// (provided by the `IntoIterator` trait). See its documentation for more.
 995 ///
 996 /// [`into_iter`]: struct.BinaryHeap.html#method.into_iter
 997 /// [`BinaryHeap`]: struct.BinaryHeap.html
 998 #[stable(feature = "rust1", since = "1.0.0")]
 999 #[derive(Clone)]
1000 pub struct IntoIter<T> {
1001     iter: vec::IntoIter<T>,
1002 }
1003
1004 #[stable(feature = "collection_debug", since = "1.17.0")]
1005 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
1006     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1007         f.debug_tuple("IntoIter")
1008          .field(&self.iter.as_slice())
1009          .finish()
1010     }
1011 }
1012
1013 #[stable(feature = "rust1", since = "1.0.0")]
1014 impl<T> Iterator for IntoIter<T> {
1015     type Item = T;
1016
1017     #[inline]
1018     fn next(&mut self) -> Option<T> {
1019         self.iter.next()
1020     }
1021
1022     #[inline]
1023     fn size_hint(&self) -> (usize, Option<usize>) {
1024         self.iter.size_hint()
1025     }
1026 }
1027
1028 #[stable(feature = "rust1", since = "1.0.0")]
1029 impl<T> DoubleEndedIterator for IntoIter<T> {
1030     #[inline]
1031     fn next_back(&mut self) -> Option<T> {
1032         self.iter.next_back()
1033     }
1034 }
1035
1036 #[stable(feature = "rust1", since = "1.0.0")]
1037 impl<T> ExactSizeIterator for IntoIter<T> {
1038     fn is_empty(&self) -> bool {
1039         self.iter.is_empty()
1040     }
1041 }
1042
1043 #[stable(feature = "fused", since = "1.26.0")]
1044 impl<T> FusedIterator for IntoIter<T> {}
1045
1046 /// A draining iterator over the elements of a `BinaryHeap`.
1047 ///
1048 /// This `struct` is created by the [`drain`] method on [`BinaryHeap`]. See its
1049 /// documentation for more.
1050 ///
1051 /// [`drain`]: struct.BinaryHeap.html#method.drain
1052 /// [`BinaryHeap`]: struct.BinaryHeap.html
1053 #[stable(feature = "drain", since = "1.6.0")]
1054 #[derive(Debug)]
1055 pub struct Drain<'a, T: 'a> {
1056     iter: vec::Drain<'a, T>,
1057 }
1058
1059 #[stable(feature = "drain", since = "1.6.0")]
1060 impl<T> Iterator for Drain<'_, T> {
1061     type Item = T;
1062
1063     #[inline]
1064     fn next(&mut self) -> Option<T> {
1065         self.iter.next()
1066     }
1067
1068     #[inline]
1069     fn size_hint(&self) -> (usize, Option<usize>) {
1070         self.iter.size_hint()
1071     }
1072 }
1073
1074 #[stable(feature = "drain", since = "1.6.0")]
1075 impl<T> DoubleEndedIterator for Drain<'_, T> {
1076     #[inline]
1077     fn next_back(&mut self) -> Option<T> {
1078         self.iter.next_back()
1079     }
1080 }
1081
1082 #[stable(feature = "drain", since = "1.6.0")]
1083 impl<T> ExactSizeIterator for Drain<'_, T> {
1084     fn is_empty(&self) -> bool {
1085         self.iter.is_empty()
1086     }
1087 }
1088
1089 #[stable(feature = "fused", since = "1.26.0")]
1090 impl<T> FusedIterator for Drain<'_, T> {}
1091
1092 #[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
1093 impl<T: Ord> From<Vec<T>> for BinaryHeap<T> {
1094     fn from(vec: Vec<T>) -> BinaryHeap<T> {
1095         let mut heap = BinaryHeap { data: vec };
1096         heap.rebuild();
1097         heap
1098     }
1099 }
1100
1101 #[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
1102 impl<T> From<BinaryHeap<T>> for Vec<T> {
1103     fn from(heap: BinaryHeap<T>) -> Vec<T> {
1104         heap.data
1105     }
1106 }
1107
1108 #[stable(feature = "rust1", since = "1.0.0")]
1109 impl<T: Ord> FromIterator<T> for BinaryHeap<T> {
1110     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> BinaryHeap<T> {
1111         BinaryHeap::from(iter.into_iter().collect::<Vec<_>>())
1112     }
1113 }
1114
1115 #[stable(feature = "rust1", since = "1.0.0")]
1116 impl<T> IntoIterator for BinaryHeap<T> {
1117     type Item = T;
1118     type IntoIter = IntoIter<T>;
1119
1120     /// Creates a consuming iterator, that is, one that moves each value out of
1121     /// the binary heap in arbitrary order. The binary heap cannot be used
1122     /// after calling this.
1123     ///
1124     /// # Examples
1125     ///
1126     /// Basic usage:
1127     ///
1128     /// ```
1129     /// use std::collections::BinaryHeap;
1130     /// let heap = BinaryHeap::from(vec![1, 2, 3, 4]);
1131     ///
1132     /// // Print 1, 2, 3, 4 in arbitrary order
1133     /// for x in heap.into_iter() {
1134     ///     // x has type i32, not &i32
1135     ///     println!("{}", x);
1136     /// }
1137     /// ```
1138     fn into_iter(self) -> IntoIter<T> {
1139         IntoIter { iter: self.data.into_iter() }
1140     }
1141 }
1142
1143 #[stable(feature = "rust1", since = "1.0.0")]
1144 impl<'a, T> IntoIterator for &'a BinaryHeap<T> {
1145     type Item = &'a T;
1146     type IntoIter = Iter<'a, T>;
1147
1148     fn into_iter(self) -> Iter<'a, T> {
1149         self.iter()
1150     }
1151 }
1152
1153 #[stable(feature = "rust1", since = "1.0.0")]
1154 impl<T: Ord> Extend<T> for BinaryHeap<T> {
1155     #[inline]
1156     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1157         <Self as SpecExtend<I>>::spec_extend(self, iter);
1158     }
1159 }
1160
1161 impl<T: Ord, I: IntoIterator<Item = T>> SpecExtend<I> for BinaryHeap<T> {
1162     default fn spec_extend(&mut self, iter: I) {
1163         self.extend_desugared(iter.into_iter());
1164     }
1165 }
1166
1167 impl<T: Ord> SpecExtend<BinaryHeap<T>> for BinaryHeap<T> {
1168     fn spec_extend(&mut self, ref mut other: BinaryHeap<T>) {
1169         self.append(other);
1170     }
1171 }
1172
1173 impl<T: Ord> BinaryHeap<T> {
1174     fn extend_desugared<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1175         let iterator = iter.into_iter();
1176         let (lower, _) = iterator.size_hint();
1177
1178         self.reserve(lower);
1179
1180         for elem in iterator {
1181             self.push(elem);
1182         }
1183     }
1184 }
1185
1186 #[stable(feature = "extend_ref", since = "1.2.0")]
1187 impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BinaryHeap<T> {
1188     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
1189         self.extend(iter.into_iter().cloned());
1190     }
1191 }