Check if an Array is a Subset of Another Array in C++

This tutorial will discuss about a unique way to check if an array is a subset of another array in C++.

Suppose we have two arrays,

int arr1[] = {72, 51, 12, 63, 54, 56, 78, 22};
int arr2[] = {63, 54, 56};

Now we want to check if the second array arr2 is a subset of first array arr1. For this, we are going to use STL algorithm std::includes() which accepts 2 ranges as arguments.

Basically std::includes() function will accept 4 arguments i.e.

• Iterator pointing to the start of first array arr1.
• Iterator pointing to the end of first array arr1.
• Iterator pointing to the start of second array arr2.
• Iterator pointing to the end of second array arr2.

It returns true if all the elements of the secondary exist in the first range.

But the important point, is that it expects both the arrays to be sorted. Therefore first we will use the std::sort() function to sort all the elements of both the arrays i.e. arr1 and arr2. Then we will use the std::includes() function to check if all the elements of second array exist in the first array or not.

Let’s see the complete example,

#include <iostream>
#include <vector>
#include <algorithm>

int main()
{
    int arr1[] = {72, 51, 12, 63, 54, 56, 78, 22};
    int arr2[] = {63, 54, 56};

    // Sort the numbers in array arr1
    std::sort(std::begin(arr1), std::end(arr1));

    // Sort the numbers in array arr2
    std::sort(std::begin(arr2), std::end(arr2));

    // Check if array arr2 includes all the elements
    // of array arr1
    bool result = std::includes(
                        std::begin(arr1),
                        std::end(arr1),
                        std::begin(arr2),
                        std::end(arr2));

    if(result)
    {
        std::cout << "Yes, Array arr2 is a subset of Array arr1" << std::endl;
    }
    else
    {
        std::cout << "No, Array arr2 is not a subset of Array arr1" << std::endl;
    }
    return 0;
}

Output :

Yes, Array arr2 is a subset of Array arr1

Summary

Today we learned about a way to check if an array is a subset of another array in C++. Thanks.