Get difference between two vectors in C++

This post will discuss how to get the difference between two vectors in C++. For vectors x and y, the solution returns all elements that are present in x, but not in y.

The recommended approach to the difference between two vectors in C+ is using the standard algorithm std::set_difference. It constructs a sorted range with the set difference of the specified sorted ranges.

The following code example demonstrates the invocation of this function. Since std::set_difference takes the sorted range, we must sort both vectors. To avoid any modifications to the vector, perform sorting on the copy of both vectors.

#include <iostream>

#include <vector>

#include <algorithm>

template<typename T>

std::vector<T> findDiff(std::vector<T> x, std::vector<T> y) { // no-ref, no-const

std::vector<T> diff;

std::sort(x.begin(), x.end());

std::sort(y.begin(), y.end());

std::set_difference(x.begin(), x.end(), y.begin(), y.end(), std::back_inserter(diff));

return diff;

}

int main()

{

std::vector<int> x = {1, 3, 5, 6, 7, 4, 8};

std::vector<int> y = {1, 2, 3, 5, 7, 8};

std::vector<int> diff = findDiff(x, y);

for (int &i: diff) {

std::cout << i << ' ';

}

return 0;

}

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Output:

4 6

To get the function return a set, use std::inserter since std::back_inserter doesn’t work on a set.

#include <iostream>

#include <vector>

#include <algorithm>

#include <unordered_set>

template<typename T>

std::unordered_set<T> findDiff(std::vector<T> x, std::vector<T> y) { // no-ref, no-const

std::unordered_set<T> diff;

std::sort(x.begin(), x.end());

std::sort(y.begin(), y.end());

std::set_difference(x.begin(), x.end(), y.begin(), y.end(),

std::inserter(diff, diff.begin()));

return diff;

}

int main()

{

std::vector<int> x = {1, 3, 5, 6, 7, 6, 4, 8};

std::vector<int> y = {1, 2, 3, 5, 7, 8};

std::unordered_set<int> diff = findDiff(x, y);

for (int i: diff) {

std::cout << i << ' ';

}

return 0;

}

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Output:

6 4

That’s all about getting the difference between two vectors in C++.

Get difference between two vectors in C++

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