src/permutations.rs


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use permutohedron::{Heap, LexicalPermutation};

pub trait PermutationGenerator {
    fn permutations(n: u32) -> Vec<Vec<u32>>;
}

pub struct HeapsPermutations;

impl PermutationGenerator for HeapsPermutations {
    fn permutations(n: u32) -> Vec<Vec<u32>> {
        Heap::<'_, Vec<u32>, _>::new(&mut (1..=n).collect()).collect()
    }
}

pub struct LexicalPermutations {
    state: Vec<u32>,
    is_ended: bool,
}

impl Iterator for LexicalPermutations {
    type Item = Vec<u32>;
    fn next(&mut self) -> Option<Self::Item> {
        if self.is_ended {
            None
        } else {
            self.is_ended = self.state.next_permutation();
            Some(self.state.clone())
        }
    }
}

impl LexicalPermutations {
    fn new(n: u32) -> Self {
        Self {
            state: (1..=n).collect(),
            is_ended: false
        }
    }
}

impl PermutationGenerator for LexicalPermutations {
    fn permutations(n: u32) -> Vec<Vec<u32>> {
        Self::new(n).collect()
    }
}