Jakub Kotur | a425e55 | 2020-12-21 17:28:15 +0100 | [diff] [blame^] | 1 | #![cfg(feature = "use_std")] |
| 2 | |
| 3 | use crate::size_hint; |
| 4 | use crate::Itertools; |
| 5 | |
| 6 | #[derive(Clone)] |
| 7 | /// An iterator adaptor that iterates over the cartesian product of |
| 8 | /// multiple iterators of type `I`. |
| 9 | /// |
| 10 | /// An iterator element type is `Vec<I>`. |
| 11 | /// |
| 12 | /// See [`.multi_cartesian_product()`](../trait.Itertools.html#method.multi_cartesian_product) |
| 13 | /// for more information. |
| 14 | #[must_use = "iterator adaptors are lazy and do nothing unless consumed"] |
| 15 | pub struct MultiProduct<I>(Vec<MultiProductIter<I>>) |
| 16 | where I: Iterator + Clone, |
| 17 | I::Item: Clone; |
| 18 | |
| 19 | /// Create a new cartesian product iterator over an arbitrary number |
| 20 | /// of iterators of the same type. |
| 21 | /// |
| 22 | /// Iterator element is of type `Vec<H::Item::Item>`. |
| 23 | pub fn multi_cartesian_product<H>(iters: H) -> MultiProduct<<H::Item as IntoIterator>::IntoIter> |
| 24 | where H: Iterator, |
| 25 | H::Item: IntoIterator, |
| 26 | <H::Item as IntoIterator>::IntoIter: Clone, |
| 27 | <H::Item as IntoIterator>::Item: Clone |
| 28 | { |
| 29 | MultiProduct(iters.map(|i| MultiProductIter::new(i.into_iter())).collect()) |
| 30 | } |
| 31 | |
| 32 | #[derive(Clone, Debug)] |
| 33 | /// Holds the state of a single iterator within a MultiProduct. |
| 34 | struct MultiProductIter<I> |
| 35 | where I: Iterator + Clone, |
| 36 | I::Item: Clone |
| 37 | { |
| 38 | cur: Option<I::Item>, |
| 39 | iter: I, |
| 40 | iter_orig: I, |
| 41 | } |
| 42 | |
| 43 | /// Holds the current state during an iteration of a MultiProduct. |
| 44 | #[derive(Debug)] |
| 45 | enum MultiProductIterState { |
| 46 | StartOfIter, |
| 47 | MidIter { on_first_iter: bool }, |
| 48 | } |
| 49 | |
| 50 | impl<I> MultiProduct<I> |
| 51 | where I: Iterator + Clone, |
| 52 | I::Item: Clone |
| 53 | { |
| 54 | /// Iterates the rightmost iterator, then recursively iterates iterators |
| 55 | /// to the left if necessary. |
| 56 | /// |
| 57 | /// Returns true if the iteration succeeded, else false. |
| 58 | fn iterate_last( |
| 59 | multi_iters: &mut [MultiProductIter<I>], |
| 60 | mut state: MultiProductIterState |
| 61 | ) -> bool { |
| 62 | use self::MultiProductIterState::*; |
| 63 | |
| 64 | if let Some((last, rest)) = multi_iters.split_last_mut() { |
| 65 | let on_first_iter = match state { |
| 66 | StartOfIter => { |
| 67 | let on_first_iter = !last.in_progress(); |
| 68 | state = MidIter { on_first_iter }; |
| 69 | on_first_iter |
| 70 | }, |
| 71 | MidIter { on_first_iter } => on_first_iter |
| 72 | }; |
| 73 | |
| 74 | if !on_first_iter { |
| 75 | last.iterate(); |
| 76 | } |
| 77 | |
| 78 | if last.in_progress() { |
| 79 | true |
| 80 | } else if MultiProduct::iterate_last(rest, state) { |
| 81 | last.reset(); |
| 82 | last.iterate(); |
| 83 | // If iterator is None twice consecutively, then iterator is |
| 84 | // empty; whole product is empty. |
| 85 | last.in_progress() |
| 86 | } else { |
| 87 | false |
| 88 | } |
| 89 | } else { |
| 90 | // Reached end of iterator list. On initialisation, return true. |
| 91 | // At end of iteration (final iterator finishes), finish. |
| 92 | match state { |
| 93 | StartOfIter => false, |
| 94 | MidIter { on_first_iter } => on_first_iter |
| 95 | } |
| 96 | } |
| 97 | } |
| 98 | |
| 99 | /// Returns the unwrapped value of the next iteration. |
| 100 | fn curr_iterator(&self) -> Vec<I::Item> { |
| 101 | self.0.iter().map(|multi_iter| { |
| 102 | multi_iter.cur.clone().unwrap() |
| 103 | }).collect() |
| 104 | } |
| 105 | |
| 106 | /// Returns true if iteration has started and has not yet finished; false |
| 107 | /// otherwise. |
| 108 | fn in_progress(&self) -> bool { |
| 109 | if let Some(last) = self.0.last() { |
| 110 | last.in_progress() |
| 111 | } else { |
| 112 | false |
| 113 | } |
| 114 | } |
| 115 | } |
| 116 | |
| 117 | impl<I> MultiProductIter<I> |
| 118 | where I: Iterator + Clone, |
| 119 | I::Item: Clone |
| 120 | { |
| 121 | fn new(iter: I) -> Self { |
| 122 | MultiProductIter { |
| 123 | cur: None, |
| 124 | iter: iter.clone(), |
| 125 | iter_orig: iter |
| 126 | } |
| 127 | } |
| 128 | |
| 129 | /// Iterate the managed iterator. |
| 130 | fn iterate(&mut self) { |
| 131 | self.cur = self.iter.next(); |
| 132 | } |
| 133 | |
| 134 | /// Reset the managed iterator. |
| 135 | fn reset(&mut self) { |
| 136 | self.iter = self.iter_orig.clone(); |
| 137 | } |
| 138 | |
| 139 | /// Returns true if the current iterator has been started and has not yet |
| 140 | /// finished; false otherwise. |
| 141 | fn in_progress(&self) -> bool { |
| 142 | self.cur.is_some() |
| 143 | } |
| 144 | } |
| 145 | |
| 146 | impl<I> Iterator for MultiProduct<I> |
| 147 | where I: Iterator + Clone, |
| 148 | I::Item: Clone |
| 149 | { |
| 150 | type Item = Vec<I::Item>; |
| 151 | |
| 152 | fn next(&mut self) -> Option<Self::Item> { |
| 153 | if MultiProduct::iterate_last( |
| 154 | &mut self.0, |
| 155 | MultiProductIterState::StartOfIter |
| 156 | ) { |
| 157 | Some(self.curr_iterator()) |
| 158 | } else { |
| 159 | None |
| 160 | } |
| 161 | } |
| 162 | |
| 163 | fn count(self) -> usize { |
| 164 | if self.0.len() == 0 { |
| 165 | return 0; |
| 166 | } |
| 167 | |
| 168 | if !self.in_progress() { |
| 169 | return self.0.into_iter().fold(1, |acc, multi_iter| { |
| 170 | acc * multi_iter.iter.count() |
| 171 | }); |
| 172 | } |
| 173 | |
| 174 | self.0.into_iter().fold( |
| 175 | 0, |
| 176 | |acc, MultiProductIter { iter, iter_orig, cur: _ }| { |
| 177 | let total_count = iter_orig.count(); |
| 178 | let cur_count = iter.count(); |
| 179 | acc * total_count + cur_count |
| 180 | } |
| 181 | ) |
| 182 | } |
| 183 | |
| 184 | fn size_hint(&self) -> (usize, Option<usize>) { |
| 185 | // Not ExactSizeIterator because size may be larger than usize |
| 186 | if self.0.len() == 0 { |
| 187 | return (0, Some(0)); |
| 188 | } |
| 189 | |
| 190 | if !self.in_progress() { |
| 191 | return self.0.iter().fold((1, Some(1)), |acc, multi_iter| { |
| 192 | size_hint::mul(acc, multi_iter.iter.size_hint()) |
| 193 | }); |
| 194 | } |
| 195 | |
| 196 | self.0.iter().fold( |
| 197 | (0, Some(0)), |
| 198 | |acc, &MultiProductIter { ref iter, ref iter_orig, cur: _ }| { |
| 199 | let cur_size = iter.size_hint(); |
| 200 | let total_size = iter_orig.size_hint(); |
| 201 | size_hint::add(size_hint::mul(acc, total_size), cur_size) |
| 202 | } |
| 203 | ) |
| 204 | } |
| 205 | |
| 206 | fn last(self) -> Option<Self::Item> { |
| 207 | let iter_count = self.0.len(); |
| 208 | |
| 209 | let lasts: Self::Item = self.0.into_iter() |
| 210 | .map(|multi_iter| multi_iter.iter.last()) |
| 211 | .while_some() |
| 212 | .collect(); |
| 213 | |
| 214 | if lasts.len() == iter_count { |
| 215 | Some(lasts) |
| 216 | } else { |
| 217 | None |
| 218 | } |
| 219 | } |
| 220 | } |