這題主要使用Hashmap，將相同size的人放在同一格hash裡，再從裡面算組數丟進答案中

class Solution {
public:
    vector<vector<int>> groupThePeople(vector<int>& groupSizes) {
        unordered_map<int, vector<int>> umap;
        for(int i = 0; i < groupSizes.size(); i++){
            umap[groupSizes[i]].push_back(i);
        }
        vector<vector<int>> ans;
        for(auto [x, v] : umap){
            int q = umap[x].size() / x;
            for(int i = 0; i < q; i++){
                vector<int> tmp;
                for(int j = 0; j < x; j++){
                    tmp.push_back(umap[x][j + i * x]);
                }
                ans.push_back(tmp);
            } 
            
        }
        return ans;
    }
};