src/libcollections/binary_heap.rs

   1 // Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! A priority queue implemented with a binary heap.
  12 //!
  13 //! Insertion and popping the largest element have `O(log n)` time complexity. Checking the largest
  14 //! element is `O(1)`. Converting a vector to a binary heap can be done in-place, and has `O(n)`
  15 //! complexity. A binary heap can also be converted to a sorted vector in-place, allowing it to
  16 //! be used for an `O(n log n)` in-place heapsort.
  17 //!
  18 //! # Examples
  19 //!
  20 //! This is a larger example that implements [Dijkstra's algorithm][dijkstra]
  21 //! to solve the [shortest path problem][sssp] on a [directed graph][dir_graph].
  22 //! It shows how to use `BinaryHeap` with custom types.
  23 //!
  24 //! [dijkstra]: http://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
  25 //! [sssp]: http://en.wikipedia.org/wiki/Shortest_path_problem
  26 //! [dir_graph]: http://en.wikipedia.org/wiki/Directed_graph
  27 //!
  28 //! ```
  29 //! use std::cmp::Ordering;
  30 //! use std::collections::BinaryHeap;
  31 //! use std::usize;
  32 //!
  33 //! #[derive(Copy, Clone, Eq, PartialEq)]
  34 //! struct State {
  35 //!     cost: usize,
  36 //!     position: usize,
  37 //! }
  38 //!
  39 //! // The priority queue depends on `Ord`.
  40 //! // Explicitly implement the trait so the queue becomes a min-heap
  41 //! // instead of a max-heap.
  42 //! impl Ord for State {
  43 //!     fn cmp(&self, other: &State) -> Ordering {
  44 //!         // Notice that the we flip the ordering here
  45 //!         other.cost.cmp(&self.cost)
  46 //!     }
  47 //! }
  48 //!
  49 //! // `PartialOrd` needs to be implemented as well.
  50 //! impl PartialOrd for State {
  51 //!     fn partial_cmp(&self, other: &State) -> Option<Ordering> {
  52 //!         Some(self.cmp(other))
  53 //!     }
  54 //! }
  55 //!
  56 //! // Each node is represented as an `usize`, for a shorter implementation.
  57 //! struct Edge {
  58 //!     node: usize,
  59 //!     cost: usize,
  60 //! }
  61 //!
  62 //! // Dijkstra's shortest path algorithm.
  63 //!
  64 //! // Start at `start` and use `dist` to track the current shortest distance
  65 //! // to each node. This implementation isn't memory-efficient as it may leave duplicate
  66 //! // nodes in the queue. It also uses `usize::MAX` as a sentinel value,
  67 //! // for a simpler implementation.
  68 //! fn shortest_path(adj_list: &Vec<Vec<Edge>>, start: usize, goal: usize) -> usize {
  69 //!     // dist[node] = current shortest distance from `start` to `node`
  70 //!     let mut dist: Vec<_> = (0..adj_list.len()).map(|_| usize::MAX).collect();
  71 //!
  72 //!     let mut heap = BinaryHeap::new();
  73 //!
  74 //!     // We're at `start`, with a zero cost
  75 //!     dist[start] = 0;
  76 //!     heap.push(State { cost: 0, position: start });
  77 //!
  78 //!     // Examine the frontier with lower cost nodes first (min-heap)
  79 //!     while let Some(State { cost, position }) = heap.pop() {
  80 //!         // Alternatively we could have continued to find all shortest paths
  81 //!         if position == goal { return cost; }
  82 //!
  83 //!         // Important as we may have already found a better way
  84 //!         if cost > dist[position] { continue; }
  85 //!
  86 //!         // For each node we can reach, see if we can find a way with
  87 //!         // a lower cost going through this node
  88 //!         for edge in adj_list[position].iter() {
  89 //!             let next = State { cost: cost + edge.cost, position: edge.node };
  90 //!
  91 //!             // If so, add it to the frontier and continue
  92 //!             if next.cost < dist[next.position] {
  93 //!                 heap.push(next);
  94 //!                 // Relaxation, we have now found a better way
  95 //!                 dist[next.position] = next.cost;
  96 //!             }
  97 //!         }
  98 //!     }
  99 //!
 100 //!     // Goal not reachable
 101 //!     usize::MAX
 102 //! }
 103 //!
 104 //! fn main() {
 105 //!     // This is the directed graph we're going to use.
 106 //!     // The node numbers correspond to the different states,
 107 //!     // and the edge weights symbolize the cost of moving
 108 //!     // from one node to another.
 109 //!     // Note that the edges are one-way.
 110 //!     //
 111 //!     //                  7
 112 //!     //          +-----------------+
 113 //!     //          |                 |
 114 //!     //          v   1        2    |
 115 //!     //          0 -----> 1 -----> 3 ---> 4
 116 //!     //          |        ^        ^      ^
 117 //!     //          |        | 1      |      |
 118 //!     //          |        |        | 3    | 1
 119 //!     //          +------> 2 -------+      |
 120 //!     //           10      |               |
 121 //!     //                   +---------------+
 122 //!     //
 123 //!     // The graph is represented as an adjacency list where each index,
 124 //!     // corresponding to a node value, has a list of outgoing edges.
 125 //!     // Chosen for its efficiency.
 126 //!     let graph = vec![
 127 //!         // Node 0
 128 //!         vec![Edge { node: 2, cost: 10 },
 129 //!              Edge { node: 1, cost: 1 }],
 130 //!         // Node 1
 131 //!         vec![Edge { node: 3, cost: 2 }],
 132 //!         // Node 2
 133 //!         vec![Edge { node: 1, cost: 1 },
 134 //!              Edge { node: 3, cost: 3 },
 135 //!              Edge { node: 4, cost: 1 }],
 136 //!         // Node 3
 137 //!         vec![Edge { node: 0, cost: 7 },
 138 //!              Edge { node: 4, cost: 2 }],
 139 //!         // Node 4
 140 //!         vec![]];
 141 //!
 142 //!     assert_eq!(shortest_path(&graph, 0, 1), 1);
 143 //!     assert_eq!(shortest_path(&graph, 0, 3), 3);
 144 //!     assert_eq!(shortest_path(&graph, 3, 0), 7);
 145 //!     assert_eq!(shortest_path(&graph, 0, 4), 5);
 146 //!     assert_eq!(shortest_path(&graph, 4, 0), usize::MAX);
 147 //! }
 148 //! ```
 149
 150 #![allow(missing_docs)]
 151 #![stable(feature = "rust1", since = "1.0.0")]
 152
 153 use core::prelude::*;
 154
 155 use core::iter::{FromIterator};
 156 use core::mem::{zeroed, replace, swap};
 157 use core::ptr;
 158
 159 use slice;
 160 use vec::{self, Vec};
 161
 162 /// A priority queue implemented with a binary heap.
 163 ///
 164 /// This will be a max-heap.
 165 ///
 166 /// It is a logic error for an item to be modified in such a way that the
 167 /// item's ordering relative to any other item, as determined by the `Ord`
 168 /// trait, changes while it is in the heap. This is normally only possible
 169 /// through `Cell`, `RefCell`, global state, I/O, or unsafe code.
 170 #[derive(Clone)]
 171 #[stable(feature = "rust1", since = "1.0.0")]
 172 pub struct BinaryHeap<T> {
 173     data: Vec<T>,
 174 }
 175
 176 #[stable(feature = "rust1", since = "1.0.0")]
 177 impl<T: Ord> Default for BinaryHeap<T> {
 178     #[inline]
 179     fn default() -> BinaryHeap<T> { BinaryHeap::new() }
 180 }
 181
 182 impl<T: Ord> BinaryHeap<T> {
 183     /// Creates an empty `BinaryHeap` as a max-heap.
 184     ///
 185     /// # Examples
 186     ///
 187     /// ```
 188     /// use std::collections::BinaryHeap;
 189     /// let mut heap = BinaryHeap::new();
 190     /// heap.push(4);
 191     /// ```
 192     #[stable(feature = "rust1", since = "1.0.0")]
 193     pub fn new() -> BinaryHeap<T> { BinaryHeap { data: vec![] } }
 194
 195     /// Creates an empty `BinaryHeap` with a specific capacity.
 196     /// This preallocates enough memory for `capacity` elements,
 197     /// so that the `BinaryHeap` does not have to be reallocated
 198     /// until it contains at least that many values.
 199     ///
 200     /// # Examples
 201     ///
 202     /// ```
 203     /// use std::collections::BinaryHeap;
 204     /// let mut heap = BinaryHeap::with_capacity(10);
 205     /// heap.push(4);
 206     /// ```
 207     #[stable(feature = "rust1", since = "1.0.0")]
 208     pub fn with_capacity(capacity: usize) -> BinaryHeap<T> {
 209         BinaryHeap { data: Vec::with_capacity(capacity) }
 210     }
 211
 212     /// Creates a `BinaryHeap` from a vector. This is sometimes called
 213     /// `heapifying` the vector.
 214     ///
 215     /// # Examples
 216     ///
 217     /// ```
 218     /// # #![feature(collections)]
 219     /// use std::collections::BinaryHeap;
 220     /// let heap = BinaryHeap::from_vec(vec![9, 1, 2, 7, 3, 2]);
 221     /// ```
 222     pub fn from_vec(vec: Vec<T>) -> BinaryHeap<T> {
 223         let mut heap = BinaryHeap { data: vec };
 224         let mut n = heap.len() / 2;
 225         while n > 0 {
 226             n -= 1;
 227             heap.sift_down(n);
 228         }
 229         heap
 230     }
 231
 232     /// Returns an iterator visiting all values in the underlying vector, in
 233     /// arbitrary order.
 234     ///
 235     /// # Examples
 236     ///
 237     /// ```
 238     /// # #![feature(collections)]
 239     /// use std::collections::BinaryHeap;
 240     /// let heap = BinaryHeap::from_vec(vec![1, 2, 3, 4]);
 241     ///
 242     /// // Print 1, 2, 3, 4 in arbitrary order
 243     /// for x in heap.iter() {
 244     ///     println!("{}", x);
 245     /// }
 246     /// ```
 247     #[stable(feature = "rust1", since = "1.0.0")]
 248     pub fn iter(&self) -> Iter<T> {
 249         Iter { iter: self.data.iter() }
 250     }
 251
 252     /// Returns the greatest item in the binary heap, or `None` if it is empty.
 253     ///
 254     /// # Examples
 255     ///
 256     /// ```
 257     /// use std::collections::BinaryHeap;
 258     /// let mut heap = BinaryHeap::new();
 259     /// assert_eq!(heap.peek(), None);
 260     ///
 261     /// heap.push(1);
 262     /// heap.push(5);
 263     /// heap.push(2);
 264     /// assert_eq!(heap.peek(), Some(&5));
 265     ///
 266     /// ```
 267     #[stable(feature = "rust1", since = "1.0.0")]
 268     pub fn peek(&self) -> Option<&T> {
 269         self.data.get(0)
 270     }
 271
 272     /// Returns the number of elements the binary heap can hold without reallocating.
 273     ///
 274     /// # Examples
 275     ///
 276     /// ```
 277     /// use std::collections::BinaryHeap;
 278     /// let mut heap = BinaryHeap::with_capacity(100);
 279     /// assert!(heap.capacity() >= 100);
 280     /// heap.push(4);
 281     /// ```
 282     #[stable(feature = "rust1", since = "1.0.0")]
 283     pub fn capacity(&self) -> usize { self.data.capacity() }
 284
 285     /// Reserves the minimum capacity for exactly `additional` more elements to be inserted in the
 286     /// given `BinaryHeap`. Does nothing if the capacity is already sufficient.
 287     ///
 288     /// Note that the allocator may give the collection more space than it requests. Therefore
 289     /// capacity can not be relied upon to be precisely minimal. Prefer `reserve` if future
 290     /// insertions are expected.
 291     ///
 292     /// # Panics
 293     ///
 294     /// Panics if the new capacity overflows `usize`.
 295     ///
 296     /// # Examples
 297     ///
 298     /// ```
 299     /// use std::collections::BinaryHeap;
 300     /// let mut heap = BinaryHeap::new();
 301     /// heap.reserve_exact(100);
 302     /// assert!(heap.capacity() >= 100);
 303     /// heap.push(4);
 304     /// ```
 305     #[stable(feature = "rust1", since = "1.0.0")]
 306     pub fn reserve_exact(&mut self, additional: usize) {
 307         self.data.reserve_exact(additional);
 308     }
 309
 310     /// Reserves capacity for at least `additional` more elements to be inserted in the
 311     /// `BinaryHeap`. The collection may reserve more space to avoid frequent reallocations.
 312     ///
 313     /// # Panics
 314     ///
 315     /// Panics if the new capacity overflows `usize`.
 316     ///
 317     /// # Examples
 318     ///
 319     /// ```
 320     /// use std::collections::BinaryHeap;
 321     /// let mut heap = BinaryHeap::new();
 322     /// heap.reserve(100);
 323     /// assert!(heap.capacity() >= 100);
 324     /// heap.push(4);
 325     /// ```
 326     #[stable(feature = "rust1", since = "1.0.0")]
 327     pub fn reserve(&mut self, additional: usize) {
 328         self.data.reserve(additional);
 329     }
 330
 331     /// Discards as much additional capacity as possible.
 332     #[stable(feature = "rust1", since = "1.0.0")]
 333     pub fn shrink_to_fit(&mut self) {
 334         self.data.shrink_to_fit();
 335     }
 336
 337     /// Removes the greatest item from the binary heap and returns it, or `None` if it
 338     /// is empty.
 339     ///
 340     /// # Examples
 341     ///
 342     /// ```
 343     /// # #![feature(collections)]
 344     /// use std::collections::BinaryHeap;
 345     /// let mut heap = BinaryHeap::from_vec(vec![1, 3]);
 346     ///
 347     /// assert_eq!(heap.pop(), Some(3));
 348     /// assert_eq!(heap.pop(), Some(1));
 349     /// assert_eq!(heap.pop(), None);
 350     /// ```
 351     #[stable(feature = "rust1", since = "1.0.0")]
 352     pub fn pop(&mut self) -> Option<T> {
 353         self.data.pop().map(|mut item| {
 354             if !self.is_empty() {
 355                 swap(&mut item, &mut self.data[0]);
 356                 self.sift_down(0);
 357             }
 358             item
 359         })
 360     }
 361
 362     /// Pushes an item onto the binary heap.
 363     ///
 364     /// # Examples
 365     ///
 366     /// ```
 367     /// use std::collections::BinaryHeap;
 368     /// let mut heap = BinaryHeap::new();
 369     /// heap.push(3);
 370     /// heap.push(5);
 371     /// heap.push(1);
 372     ///
 373     /// assert_eq!(heap.len(), 3);
 374     /// assert_eq!(heap.peek(), Some(&5));
 375     /// ```
 376     #[stable(feature = "rust1", since = "1.0.0")]
 377     pub fn push(&mut self, item: T) {
 378         let old_len = self.len();
 379         self.data.push(item);
 380         self.sift_up(0, old_len);
 381     }
 382
 383     /// Pushes an item onto the binary heap, then pops the greatest item off the queue in
 384     /// an optimized fashion.
 385     ///
 386     /// # Examples
 387     ///
 388     /// ```
 389     /// # #![feature(collections)]
 390     /// use std::collections::BinaryHeap;
 391     /// let mut heap = BinaryHeap::new();
 392     /// heap.push(1);
 393     /// heap.push(5);
 394     ///
 395     /// assert_eq!(heap.push_pop(3), 5);
 396     /// assert_eq!(heap.push_pop(9), 9);
 397     /// assert_eq!(heap.len(), 2);
 398     /// assert_eq!(heap.peek(), Some(&3));
 399     /// ```
 400     pub fn push_pop(&mut self, mut item: T) -> T {
 401         match self.data.get_mut(0) {
 402             None => return item,
 403             Some(top) => if *top > item {
 404                 swap(&mut item, top);
 405             } else {
 406                 return item;
 407             },
 408         }
 409
 410         self.sift_down(0);
 411         item
 412     }
 413
 414     /// Pops the greatest item off the binary heap, then pushes an item onto the queue in
 415     /// an optimized fashion. The push is done regardless of whether the binary heap
 416     /// was empty.
 417     ///
 418     /// # Examples
 419     ///
 420     /// ```
 421     /// # #![feature(collections)]
 422     /// use std::collections::BinaryHeap;
 423     /// let mut heap = BinaryHeap::new();
 424     ///
 425     /// assert_eq!(heap.replace(1), None);
 426     /// assert_eq!(heap.replace(3), Some(1));
 427     /// assert_eq!(heap.len(), 1);
 428     /// assert_eq!(heap.peek(), Some(&3));
 429     /// ```
 430     pub fn replace(&mut self, mut item: T) -> Option<T> {
 431         if !self.is_empty() {
 432             swap(&mut item, &mut self.data[0]);
 433             self.sift_down(0);
 434             Some(item)
 435         } else {
 436             self.push(item);
 437             None
 438         }
 439     }
 440
 441     /// Consumes the `BinaryHeap` and returns the underlying vector
 442     /// in arbitrary order.
 443     ///
 444     /// # Examples
 445     ///
 446     /// ```
 447     /// # #![feature(collections)]
 448     /// use std::collections::BinaryHeap;
 449     /// let heap = BinaryHeap::from_vec(vec![1, 2, 3, 4, 5, 6, 7]);
 450     /// let vec = heap.into_vec();
 451     ///
 452     /// // Will print in some order
 453     /// for x in vec.iter() {
 454     ///     println!("{}", x);
 455     /// }
 456     /// ```
 457     pub fn into_vec(self) -> Vec<T> { self.data }
 458
 459     /// Consumes the `BinaryHeap` and returns a vector in sorted
 460     /// (ascending) order.
 461     ///
 462     /// # Examples
 463     ///
 464     /// ```
 465     /// # #![feature(collections)]
 466     /// use std::collections::BinaryHeap;
 467     ///
 468     /// let mut heap = BinaryHeap::from_vec(vec![1, 2, 4, 5, 7]);
 469     /// heap.push(6);
 470     /// heap.push(3);
 471     ///
 472     /// let vec = heap.into_sorted_vec();
 473     /// assert_eq!(vec, [1, 2, 3, 4, 5, 6, 7]);
 474     /// ```
 475     pub fn into_sorted_vec(mut self) -> Vec<T> {
 476         let mut end = self.len();
 477         while end > 1 {
 478             end -= 1;
 479             self.data.swap(0, end);
 480             self.sift_down_range(0, end);
 481         }
 482         self.into_vec()
 483     }
 484
 485     // The implementations of sift_up and sift_down use unsafe blocks in
 486     // order to move an element out of the vector (leaving behind a
 487     // zeroed element), shift along the others and move it back into the
 488     // vector over the junk element. This reduces the constant factor
 489     // compared to using swaps, which involves twice as many moves.
 490     fn sift_up(&mut self, start: usize, mut pos: usize) {
 491         unsafe {
 492             let new = replace(&mut self.data[pos], zeroed());
 493
 494             while pos > start {
 495                 let parent = (pos - 1) >> 1;
 496
 497                 if new <= self.data[parent] { break; }
 498
 499                 let x = replace(&mut self.data[parent], zeroed());
 500                 ptr::write(&mut self.data[pos], x);
 501                 pos = parent;
 502             }
 503             ptr::write(&mut self.data[pos], new);
 504         }
 505     }
 506
 507     fn sift_down_range(&mut self, mut pos: usize, end: usize) {
 508         unsafe {
 509             let start = pos;
 510             let new = replace(&mut self.data[pos], zeroed());
 511
 512             let mut child = 2 * pos + 1;
 513             while child < end {
 514                 let right = child + 1;
 515                 if right < end && !(self.data[child] > self.data[right]) {
 516                     child = right;
 517                 }
 518                 let x = replace(&mut self.data[child], zeroed());
 519                 ptr::write(&mut self.data[pos], x);
 520                 pos = child;
 521                 child = 2 * pos + 1;
 522             }
 523
 524             ptr::write(&mut self.data[pos], new);
 525             self.sift_up(start, pos);
 526         }
 527     }
 528
 529     fn sift_down(&mut self, pos: usize) {
 530         let len = self.len();
 531         self.sift_down_range(pos, len);
 532     }
 533
 534     /// Returns the length of the binary heap.
 535     #[stable(feature = "rust1", since = "1.0.0")]
 536     pub fn len(&self) -> usize { self.data.len() }
 537
 538     /// Checks if the binary heap is empty.
 539     #[stable(feature = "rust1", since = "1.0.0")]
 540     pub fn is_empty(&self) -> bool { self.len() == 0 }
 541
 542     /// Clears the binary heap, returning an iterator over the removed elements.
 543     ///
 544     /// The elements are removed in arbitrary order.
 545     #[inline]
 546     #[unstable(feature = "collections",
 547                reason = "matches collection reform specification, waiting for dust to settle")]
 548     pub fn drain(&mut self) -> Drain<T> {
 549         Drain { iter: self.data.drain() }
 550     }
 551
 552     /// Drops all items from the binary heap.
 553     #[stable(feature = "rust1", since = "1.0.0")]
 554     pub fn clear(&mut self) { self.drain(); }
 555 }
 556
 557 /// `BinaryHeap` iterator.
 558 #[stable(feature = "rust1", since = "1.0.0")]
 559 pub struct Iter <'a, T: 'a> {
 560     iter: slice::Iter<'a, T>,
 561 }
 562
 563 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
 564 #[stable(feature = "rust1", since = "1.0.0")]
 565 impl<'a, T> Clone for Iter<'a, T> {
 566     fn clone(&self) -> Iter<'a, T> {
 567         Iter { iter: self.iter.clone() }
 568     }
 569 }
 570
 571 #[stable(feature = "rust1", since = "1.0.0")]
 572 impl<'a, T> Iterator for Iter<'a, T> {
 573     type Item = &'a T;
 574
 575     #[inline]
 576     fn next(&mut self) -> Option<&'a T> { self.iter.next() }
 577
 578     #[inline]
 579     fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
 580 }
 581
 582 #[stable(feature = "rust1", since = "1.0.0")]
 583 impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
 584     #[inline]
 585     fn next_back(&mut self) -> Option<&'a T> { self.iter.next_back() }
 586 }
 587
 588 #[stable(feature = "rust1", since = "1.0.0")]
 589 impl<'a, T> ExactSizeIterator for Iter<'a, T> {}
 590
 591 /// An iterator that moves out of a `BinaryHeap`.
 592 #[stable(feature = "rust1", since = "1.0.0")]
 593 pub struct IntoIter<T> {
 594     iter: vec::IntoIter<T>,
 595 }
 596
 597 #[stable(feature = "rust1", since = "1.0.0")]
 598 impl<T> Iterator for IntoIter<T> {
 599     type Item = T;
 600
 601     #[inline]
 602     fn next(&mut self) -> Option<T> { self.iter.next() }
 603
 604     #[inline]
 605     fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
 606 }
 607
 608 #[stable(feature = "rust1", since = "1.0.0")]
 609 impl<T> DoubleEndedIterator for IntoIter<T> {
 610     #[inline]
 611     fn next_back(&mut self) -> Option<T> { self.iter.next_back() }
 612 }
 613
 614 #[stable(feature = "rust1", since = "1.0.0")]
 615 impl<T> ExactSizeIterator for IntoIter<T> {}
 616
 617 /// An iterator that drains a `BinaryHeap`.
 618 #[unstable(feature = "collections", reason = "recent addition")]
 619 pub struct Drain<'a, T: 'a> {
 620     iter: vec::Drain<'a, T>,
 621 }
 622
 623 #[stable(feature = "rust1", since = "1.0.0")]
 624 impl<'a, T: 'a> Iterator for Drain<'a, T> {
 625     type Item = T;
 626
 627     #[inline]
 628     fn next(&mut self) -> Option<T> { self.iter.next() }
 629
 630     #[inline]
 631     fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
 632 }
 633
 634 #[stable(feature = "rust1", since = "1.0.0")]
 635 impl<'a, T: 'a> DoubleEndedIterator for Drain<'a, T> {
 636     #[inline]
 637     fn next_back(&mut self) -> Option<T> { self.iter.next_back() }
 638 }
 639
 640 #[stable(feature = "rust1", since = "1.0.0")]
 641 impl<'a, T: 'a> ExactSizeIterator for Drain<'a, T> {}
 642
 643 #[stable(feature = "rust1", since = "1.0.0")]
 644 impl<T: Ord> FromIterator<T> for BinaryHeap<T> {
 645     fn from_iter<I: IntoIterator<Item=T>>(iter: I) -> BinaryHeap<T> {
 646         BinaryHeap::from_vec(iter.into_iter().collect())
 647     }
 648 }
 649
 650 #[stable(feature = "rust1", since = "1.0.0")]
 651 impl<T: Ord> IntoIterator for BinaryHeap<T> {
 652     type Item = T;
 653     type IntoIter = IntoIter<T>;
 654
 655     /// Creates a consuming iterator, that is, one that moves each value out of
 656     /// the binary heap in arbitrary order. The binary heap cannot be used
 657     /// after calling this.
 658     ///
 659     /// # Examples
 660     ///
 661     /// ```
 662     /// # #![feature(collections)]
 663     /// use std::collections::BinaryHeap;
 664     /// let heap = BinaryHeap::from_vec(vec![1, 2, 3, 4]);
 665     ///
 666     /// // Print 1, 2, 3, 4 in arbitrary order
 667     /// for x in heap.into_iter() {
 668     ///     // x has type i32, not &i32
 669     ///     println!("{}", x);
 670     /// }
 671     /// ```
 672     fn into_iter(self) -> IntoIter<T> {
 673         IntoIter { iter: self.data.into_iter() }
 674     }
 675 }
 676
 677 #[stable(feature = "rust1", since = "1.0.0")]
 678 impl<'a, T> IntoIterator for &'a BinaryHeap<T> where T: Ord {
 679     type Item = &'a T;
 680     type IntoIter = Iter<'a, T>;
 681
 682     fn into_iter(self) -> Iter<'a, T> {
 683         self.iter()
 684     }
 685 }
 686
 687 #[stable(feature = "rust1", since = "1.0.0")]
 688 impl<T: Ord> Extend<T> for BinaryHeap<T> {
 689     fn extend<I: IntoIterator<Item=T>>(&mut self, iterable: I) {
 690         let iter = iterable.into_iter();
 691         let (lower, _) = iter.size_hint();
 692
 693         self.reserve(lower);
 694
 695         for elem in iter {
 696             self.push(elem);
 697         }
 698     }
 699 }