Convert a vector to a set in C++

This post will discuss how to convert a vector to a set in C++.

1. Naive Solution

We can also write our own routine for converting a vector to a set. The idea is very simple – create an empty set, traverse the vector using a range-based for-loop and insert each encountered element into the set.

#include <iostream>

#include <vector>

#include <unordered_set>

int main()

{

std::vector<int> input({ 1, 2, 2, 1, 3, 1, 4 });

std::unordered_set<int> set;

for (const int &i: input) {

set.insert(i);

}

for (const int &i: set) {

std::cout << i << " ";

}

return 0;

}

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Output:

4 3 2 1

2. Using Range Constructor

An efficient solution is to pass two input iterators pointing to the beginning and end of the given vector to the constructor of the set class.

#include <iostream>

#include <vector>

#include <unordered_set>

int main()

{

std::vector<int> input({ 1, 2, 2, 1, 3, 1, 4 });

std::unordered_set<int> set(input.begin(), input.end());

for (const int &i: set) {

std::cout << i << " ";

}

return 0;

}

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Output:

4 3 2 1

3. Using `std::copy` function

If we need to copy the vector elements to an existing set, the recommended approach is to use the standard algorithm std::copy defined in the <algorithm> header.

#include <iostream>

#include <vector>

#include <algorithm>

#include <unordered_set>

int main()

{

std::vector<int> input({ 1, 2, 2, 1, 3, 1, 4 });

std::unordered_set<int> set;

std::copy(input.begin(),

input.end(),

std::inserter(set, set.end()));

for (const int &i: set) {

std::cout << i << " ";

}

return 0;

}

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Output:

4 3 2 1

That’s all about converting a vector to a set in C++.

Convert a vector to a set in C++

1. Naive Solution

2. Using Range Constructor

3. Using std::copy function

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3. Using `std::copy` function