1282. Group the People Given the Group Size They Belong To

Problem Statement

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.

Example 1:

Input: groupSizes = [3,3,3,3,3,1,3]
Output: [[5],[0,1,2],[3,4,6]]
Explanation: 
The first group is [5]. The size is 1, and groupSizes[5] = 1.
The second group is [0,1,2]. The size is 3, and groupSizes[0] = groupSizes[1] = groupSizes[2] = 3.
The third group is [3,4,6]. The size is 3, and groupSizes[3] = groupSizes[4] = groupSizes[6] = 3.
Other possible solutions are [[2,1,6],[5],[0,4,3]] and [[5],[0,6,2],[4,3,1]].

Example 2:

Input: groupSizes = [2,1,3,3,3,2]
Output: [[1],[0,5],[2,3,4]]

Constraints:

groupSizes.length == n
1 <= n <= 500
1 <= groupSizes[i] <= n

Intuition

Make a map and store the vector

Video Links

Approach 1:

C++

class Solution {
public:
    vector<vector<int>> groupThePeople(vector<int>& arr) {
        map<int, vector<int>> mp;
        vector<vector<int>> ans;

        for(int i=0; i<arr.size(); i++){
            int group_size = arr[i];
            mp[group_size].push_back(i);

            if(mp[group_size].size() == group_size){
                ans.push_back(mp[group_size]);
                mp.erase(group_size);
            }
        }

        return ans;
    }
};

Approach 2:

C++

Approach 3:

C++

Approach 4:

C++