vendor/itertools-0.8.2/src/combinations_with_replacement.rs

   1 use std::fmt;
   2
   3 use super::lazy_buffer::LazyBuffer;
   4
   5 /// An iterator to iterate through all the `n`-length combinations in an iterator, with replacement.
   6 ///
   7 /// See [`.combinations_with_replacement()`](../trait.Itertools.html#method.combinations_with_replacement) for more information.
   8 #[derive(Clone)]
   9 pub struct CombinationsWithReplacement<I>
  10 where
  11     I: Iterator,
  12     I::Item: Clone,
  13 {
  14     k: usize,
  15     indices: Vec<usize>,
  16     // The current known max index value. This increases as pool grows.
  17     max_index: usize,
  18     pool: LazyBuffer<I>,
  19     first: bool,
  20 }
  21
  22 impl<I> fmt::Debug for CombinationsWithReplacement<I>
  23 where
  24     I: Iterator + fmt::Debug,
  25     I::Item: fmt::Debug + Clone,
  26 {
  27     debug_fmt_fields!(Combinations, k, indices, max_index, pool, first);
  28 }
  29
  30 impl<I> CombinationsWithReplacement<I>
  31 where
  32     I: Iterator,
  33     I::Item: Clone,
  34 {
  35     /// Map the current mask over the pool to get an output combination
  36     fn current(&self) -> Vec<I::Item> {
  37         self.indices.iter().map(|i| self.pool[*i].clone()).collect()
  38     }
  39 }
  40
  41 /// Create a new `CombinationsWithReplacement` from a clonable iterator.
  42 pub fn combinations_with_replacement<I>(iter: I, k: usize) -> CombinationsWithReplacement<I>
  43 where
  44     I: Iterator,
  45     I::Item: Clone,
  46 {
  47     let indices: Vec<usize> = vec![0; k];
  48     let pool: LazyBuffer<I> = LazyBuffer::new(iter);
  49
  50     CombinationsWithReplacement {
  51         k,
  52         indices,
  53         max_index: 0,
  54         pool: pool,
  55         first: true,
  56     }
  57 }
  58
  59 impl<I> Iterator for CombinationsWithReplacement<I>
  60 where
  61     I: Iterator,
  62     I::Item: Clone,
  63 {
  64     type Item = Vec<I::Item>;
  65     fn next(&mut self) -> Option<Self::Item> {
  66         // If this is the first iteration, return early
  67         if self.first {
  68             // In empty edge cases, stop iterating immediately
  69             return if self.k == 0 || self.pool.is_done() {
  70                 None
  71             // Otherwise, yield the initial state
  72             } else {
  73                 self.first = false;
  74                 Some(self.current())
  75             };
  76         }
  77
  78         // Check if we need to consume more from the iterator
  79         // This will run while we increment our first index digit
  80         if !self.pool.is_done() {
  81             self.pool.get_next();
  82             self.max_index = self.pool.len() - 1;
  83         }
  84
  85         // Work out where we need to update our indices
  86         let mut increment: Option<(usize, usize)> = None;
  87         for (i, indices_int) in self.indices.iter().enumerate().rev() {
  88             if indices_int < &self.max_index {
  89                 increment = Some((i, indices_int + 1));
  90                 break;
  91             }
  92         }
  93
  94         match increment {
  95             // If we can update the indices further
  96             Some((increment_from, increment_value)) => {
  97                 // We need to update the rightmost non-max value
  98                 // and all those to the right
  99                 for indices_index in increment_from..self.indices.len() {
 100                     self.indices[indices_index] = increment_value
 101                 }
 102                 Some(self.current())
 103             }
 104             // Otherwise, we're done
 105             None => None,
 106         }
 107     }
 108 }