Variable Sized Arrays in C++ HackerRank solution

Consider an n-element array, a, where each index i in the array contains a reference to an array of   K_i integers (where the value of K_i varies from array to array). See the Explanation section below for a diagram.

Given a, you must answer  q queries. Each query is in the format i j, where i denotes an index in array  and  denotes an index in the array located at a[i]. For each query, find and print the value of element j in the array at location a[i] on a new line.

Input Format

The first line contains two space-separated integers denoting the respective values of n (the number of variable-length arrays) and q (the number of queries).

Each line i of the n subsequent lines contains a space-separated sequence in the format k a[i]0 a[i]1 … a[i]K_-1 describing the K element array located at a[i].

Each of the q subsequent lines contains two space-separated integers describing the respective values of  i(an index in array a) and j(an index in the array referenced by a[i]) for a query.

Constraints

• All indices in this challenge are zero-based.
• All the given numbers are non negative and are not greater than 10⁶

Output Format

For each pair of i and j values (i.e., for each query), print a single integer that denotes the element located at index j of the array referenced by a[i]. There should be a total of q lines of output.

Sample Input

2 2
3 1 5 4
5 1 2 8 9 3
0 1
1 3

Sample Output

5
9

Explanation

The diagram below depicts our assembled Sample Input:

We perform the following q=2 queries:

Find the array located at index i=0, which corresponds to a[0]=[1,5,4]. We must print the value at index j=1 of this array which, as you can see, is 5.

Find the array located at index i=1 , which corresponds to a[1]=[1,2,8,9,3]. We must print the value at index j=3 of this array which, as you can see, is 9 .

Solution

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
    int n;
    int q;
    cin >> n >> q;
    vector<int> a[n];
    for(int i = 0; i < n; i++){
        int m;
        cin >> m;
        int o;
        for(int j = 0; j < m; j++){
            cin >> o;
            a[i].push_back(o);
        }
    }
    
    int r, s;
    for(int k = 1; k <= q; k++){
        cin >> r >> s;
        cout << a[r][s] << endl;
    }
    return 0;
}