Check out example codes for "variable sized arrays hackerrank". It will help you in understanding the concepts better.

Code Example 1

int n,q; cin >> n >> q; vector< vector<int> > a(n);  // input each array for (int i=0;i<n;i++) {     int k;     cin >> k;      for (int j=0;j<k;j++) {         int data;         cin >> data;         a[i].push_back(data);     } }  // do the queries for (int i=0;i<q;i++) {     int x,y;     cin >> x >> y;     cout << a[x][y] << endl; }

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