110 lines
3.0 KiB
Rust
110 lines
3.0 KiB
Rust
use alloc::vec::Vec;
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use std::fmt;
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use std::iter::FusedIterator;
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use super::lazy_buffer::LazyBuffer;
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/// An iterator to iterate through all the `n`-length combinations in an iterator, with replacement.
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///
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/// See [`.combinations_with_replacement()`](crate::Itertools::combinations_with_replacement)
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/// for more information.
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#[derive(Clone)]
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pub struct CombinationsWithReplacement<I>
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where
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I: Iterator,
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I::Item: Clone,
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{
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indices: Vec<usize>,
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pool: LazyBuffer<I>,
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first: bool,
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}
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impl<I> fmt::Debug for CombinationsWithReplacement<I>
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where
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I: Iterator + fmt::Debug,
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I::Item: fmt::Debug + Clone,
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{
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debug_fmt_fields!(Combinations, indices, pool, first);
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}
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impl<I> CombinationsWithReplacement<I>
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where
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I: Iterator,
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I::Item: Clone,
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{
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/// Map the current mask over the pool to get an output combination
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fn current(&self) -> Vec<I::Item> {
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self.indices.iter().map(|i| self.pool[*i].clone()).collect()
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}
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}
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/// Create a new `CombinationsWithReplacement` from a clonable iterator.
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pub fn combinations_with_replacement<I>(iter: I, k: usize) -> CombinationsWithReplacement<I>
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where
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I: Iterator,
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I::Item: Clone,
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{
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let indices: Vec<usize> = alloc::vec![0; k];
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let pool: LazyBuffer<I> = LazyBuffer::new(iter);
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CombinationsWithReplacement {
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indices,
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pool,
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first: true,
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}
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}
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impl<I> Iterator for CombinationsWithReplacement<I>
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where
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I: Iterator,
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I::Item: Clone,
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{
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type Item = Vec<I::Item>;
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fn next(&mut self) -> Option<Self::Item> {
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// If this is the first iteration, return early
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if self.first {
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// In empty edge cases, stop iterating immediately
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return if self.indices.len() != 0 && !self.pool.get_next() {
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None
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// Otherwise, yield the initial state
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} else {
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self.first = false;
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Some(self.current())
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};
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}
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// Check if we need to consume more from the iterator
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// This will run while we increment our first index digit
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self.pool.get_next();
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// Work out where we need to update our indices
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let mut increment: Option<(usize, usize)> = None;
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for (i, indices_int) in self.indices.iter().enumerate().rev() {
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if *indices_int < self.pool.len()-1 {
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increment = Some((i, indices_int + 1));
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break;
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}
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}
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match increment {
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// If we can update the indices further
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Some((increment_from, increment_value)) => {
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// We need to update the rightmost non-max value
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// and all those to the right
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for indices_index in increment_from..self.indices.len() {
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self.indices[indices_index] = increment_value
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}
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Some(self.current())
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}
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// Otherwise, we're done
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None => None,
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}
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}
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}
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impl<I> FusedIterator for CombinationsWithReplacement<I>
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where
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I: Iterator,
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I::Item: Clone,
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{}
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