Group the people given the group size they belong to

Array Hash Table Greedy

87.5% acceptance

Feb 25, 2026

3156

747

There are n people that are split into some unknown number of groups. Each person is labeled with a unique ID from 0 to n - 1. You are given an integer array groupSizes, where groupSizes[i] is the size of the group that person i is in. For example, if groupSizes[1] = 3, then person 1 must be in a group of size 3. Return a list of groups such that each person i is in a group of size groupSizes[i]. Each person should appear in exactly one group, and every person must be in a group. If there are multiple answers, return any of them. It is guaranteed that there will be at least one valid solution for the given input.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn group_the_people(group_sizes: Vec<i32>) -> Vec<Vec<i32>> {
    use std::collections::HashMap;
    let mut buckets: HashMap<i32, Vec<i32>> = HashMap::new();
    let mut result = vec![];

    for (i, &gs) in group_sizes.iter().enumerate() {
      let group = buckets.entry(gs).or_default();
      group.push(i as i32);
      if group.len() == gs as usize {
        result.push(group.clone());
        group.clear();
      }
    }
    result
  }
}