use std::collections::{HashMap, HashSet, VecDeque};

impl Solution {
    fn from_managers(managers: &[i32]) -> HashMap<usize, HashSet<usize>> {
        let mut mapping = HashMap::new();

        for (i, manager) in managers
            .iter()
            .enumerate()
            .filter(|&(_, &manager)| manager != -1)
        {
            mapping
                .entry(*manager as usize)
                .or_insert_with(HashSet::new)
                .insert(i);
        }

        mapping
    }

    pub fn num_of_minutes(_n: i32, head_id: i32, manager: Vec<i32>, inform_time: Vec<i32>) -> i32 {
        let manager_mapping = Solution::from_managers(&manager);

        let mut q = VecDeque::new();
        q.push_back((head_id as usize, 0));

        let mut minutes = -1;
        while let Some((manager, t)) = q.pop_front() {
            minutes = std::cmp::max(minutes, t);

            for employee in manager_mapping.get(&manager).unwrap_or(&HashSet::new()) {
                q.push_back((*employee, t + inform_time[manager]));
            }
        }
        minutes
    }
}