Task and Solution : Variable Sized Arrays of HackerRank

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

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

Click here to know more about how to create variable sized arrays in C++.

Input Format

The first line contains two space-separated integers denoting the respective values of  (the number of variable-length arrays) and  (the number of queries).
Each line  of the  subsequent lines contains a space-separated sequence in the format k a[i]0 a[i]1 … a[i]k-1 describing the -element array located at .
Each of the  subsequent lines contains two space-separated integers describing the respective values of  (an index in array ) and  (an index in the array referenced by ) for a query.

Constraints

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

Output Format

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

1. Find the array located at index , which corresponds to . We must print the value at index  of this array which, as you can see, is .
2. Find the array located at index , which corresponds to . We must print the value at index  of this array which, as you can see, is .

Solution

#include <iostream>

#include <vector>

using namespace std;

int main() {

    int q, n, i, j;

    cin >> q >> n;

    // Create a vector of vectors to represent the 2D array

    vector<vector<int>> a(n);

    // Read the input array values

    for (int k = 0; k < n; k++) {

        int size;

        cin >> size;

        a[k].resize(size);

        for (int l = 0; l < size; l++) {

            cin >> a[k][l];

        }

    }

    // Process the queries

    for (int m = 0; m < q; m++) {

        cin >> i >> j;

        cout << a[i][j] << endl;

    }

    return 0;

}

Source : HackerRank