adventofcode2024/day_07/src/equation/operator_set.rs

use std::collections::HashMap;
use std::collections::HashSet;
use std::sync::{LazyLock, Mutex};

#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
pub enum Op {
    Multiply,
    Add,
}

type OperatorCache = HashMap<usize, HashSet<Vec<Op>>>;

static OPERATOR_SET_CACHE: LazyLock<Mutex<OperatorCache>> =
    LazyLock::new(|| Mutex::new(HashMap::new()));

fn check_operator_set_cache(cache_key: usize) -> Option<HashSet<Vec<Op>>> {
    OPERATOR_SET_CACHE.lock().unwrap().get(&cache_key).cloned()
}

fn store_operator_set_in_cache(cache_key: usize, cache_value: HashSet<Vec<Op>>) {
    OPERATOR_SET_CACHE
        .lock()
        .unwrap()
        .insert(cache_key, cache_value);
}

fn create_operator_set_recurse(
    operators_permutation_set: &mut HashSet<Vec<Op>>,
    operators: Vec<Op>,
) {
    operators_permutation_set.insert(operators.clone());
    if !operators.contains(&Op::Add) {
        return;
    }

    for i in 0..operators.len() {
        if operators[i] == Op::Multiply {
            break;
        }
        let mut new_operators = operators.clone();
        new_operators[i] = Op::Multiply;
        create_operator_set_recurse(operators_permutation_set, new_operators);
    }
}

pub fn create_operator_set(num_of_operators: usize) -> HashSet<Vec<Op>> {
    // Check cache
    if let Some(cached_value) = check_operator_set_cache(num_of_operators) {
        return cached_value.clone();
    }

    let mut operator_sets: HashSet<Vec<Op>> = HashSet::new();
    create_operator_set_recurse(&mut operator_sets, vec![Op::Add; num_of_operators]);

    // Store value in cache
    store_operator_set_in_cache(num_of_operators, operator_sets.clone());

    operator_sets
}

fn create_permutations_recurse(
    values: &HashSet<Op>,
    len: usize,
    permutations: &mut HashSet<Vec<Op>>,
    curr_permutation: Vec<Op>,
) {
    if curr_permutation.len() == len {
        permutations.insert(curr_permutation);
        return;
    }

    for v in values {
        let mut next_permutation = curr_permutation.clone();
        next_permutation.push(*v);
        create_permutations_recurse(values, len, permutations, next_permutation);
    }
}

pub fn create_permutations(set: HashSet<Op>, len: usize) -> HashSet<Vec<Op>> {
    let mut permutations = HashSet::new();
    create_permutations_recurse(&set, len, &mut permutations, vec![]);
    permutations
}