adventofcode2024/day_07/src/equation/operator_set.rs

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

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

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

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

    for i in 0..operators.len() {
        if operators[i] {
            continue;
        }
        let mut new_operators = operators.clone();
        new_operators[i] = true;
        create_operator_set_recurse(operators_permutation_set, new_operators);
    }
}

pub fn create_operator_set(num_of_operators: usize) -> HashSet<Vec<bool>> {
    {
        // Check cache
        if let Some(cached_value) = OPERATOR_SET_CACHE.lock().unwrap().get(&num_of_operators) {
            return cached_value.clone();
        }
    }
    let mut operator_sets: HashSet<Vec<bool>> = HashSet::new();
    create_operator_set_recurse(&mut operator_sets, vec![false; num_of_operators]);
    {
        // Store value in cache
        OPERATOR_SET_CACHE
            .lock()
            .unwrap()
            .insert(num_of_operators, operator_sets.clone());
    }
    operator_sets
}