Reverse a vector in C++

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

Practice this problem

1. Using `std::reverse` function

The simplest solution is to use the std::reverse function defined in the <algorithm> header. This function internally uses std::iter_swap for swapping the elements from both ends of the given range.

#include <iostream>

#include <vector>

#include <algorithm>

template <typename T>

std::ostream &operator<<(std::ostream &os, const std::vector<T> &v)

{

for (T const &i: v) {

os << i << " ";

}

return os;

}

int main()

{

std::vector<int> v = { 1, 2, 3, 4, 5 };

std::cout << "Original Vector: " << v << std::endl;

std::reverse(v.begin(), v.end());

std::cout << "Reversed Vector: " << v << std::endl;

return 0;

}

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Output:

Original Vector: 1 2 3 4 5
Reversed Vector: 5 4 3 2 1

2. Using Reverse Iterators

Here, the idea is to use reverse iterators to construct a new vector using its range constructor. Then we can simply swap the original vector with the new vector.

#include <iostream>

#include <vector>

#include <algorithm>

template <typename T>

std::ostream& operator<<(std::ostream& os, const std::vector<T> &v)

{

for (T const& i: v) {

os << i << " ";

}

return os;

}

int main()

{

std::vector<int> v = { 1, 2, 3, 4, 5 };

std::cout << "Original Vector: " << v << std::endl;

std::vector<int> r(v.rbegin(), v.rend());

v.swap(r); // or, call `v = r`

std::cout << "Reversed Vector: " << v << std::endl;

return 0;

}

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3. Using `std::swap` function

We have seen that std::reverse function internally uses std::iter_swap function. The same can be achieved with the help of the std::swap function, as shown below:

#include <iostream>

#include <vector>

#include <algorithm>

template <typename T>

std::ostream& operator<<(std::ostream& os, const std::vector<T> &v)

{

for (T const& i: v) {

os << i << " ";

}

return os;

}

int main()

{

std::vector<int> v = { 1, 2, 3, 4, 5 };

std::cout << "Original Vector: " << v << std::endl;

for (auto start = v.begin(), end = std::prev(v.end());

start < end; ++start, --end) {

std::swap(*start, *end);

}

std::cout << "Reversed Vector: " << v << std::endl;

return 0;

}

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4. Using `std::transform` function

Finally, another good solution is to use the std::transform algorithm, as shown below:

#include <iostream>

#include <vector>

#include <algorithm>

template <typename T>

std::ostream& operator<<(std::ostream& os, const std::vector<T> &v)

{

for (T const& i: v) {

os << i << " ";

}

return os;

}

int main()

{

std::vector<int> v = { 1, 2, 3, 4, 5 };

std::cout << "Original Vector: " << v << std::endl;

auto mid = v.begin() + v.size()/2;

std::transform(v.begin(), mid,

v.rbegin(), v.begin(),

[](int &x, int &y)

{

std::swap(x, y);

return x;

});

std::cout << "Reversed Vector: " << v << std::endl;

return 0;

}

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That’s all about reversing a vector in C++.

1. Using std::reverse function

2. Using Reverse Iterators

3. Using std::swap function

4. Using std::transform function

Share this:

1. Using `std::reverse` function

3. Using `std::swap` function

4. Using `std::transform` function