std::rotate

 

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Defined in header <algorithm>
template< class ForwardIt > void rotate( ForwardIt first, ForwardIt n_first, ForwardIt last );		(until C++11)
template< class ForwardIt > ForwardIt rotate( ForwardIt first, ForwardIt n_first, ForwardIt last );		(since C++11)

Performs a left rotation on a range of elements.

Specifically, std::rotate swaps the elements in the range [first, last) in such a way that the element n_first becomes the first element of the new range and n_first - 1 becomes the last element.

A precondition of this function is that [first, n_first) and [n_first, last) are valid ranges.

Parameters

first	-	the beginning of the original range
n_first	-	the element that should appear at the beginning of the rotated range
last	-	the end of the original range
Type requirements
- ForwardIt must meet the requirements of ValueSwappable and ForwardIterator.
- The type of dereferenced ForwardIt must meet the requirements of MoveAssignable and MoveConstructible.

Return value

(none)	(until C++11)
The iterator equal to first + (last - n_first)	(since C++11)

Complexity

Linear in the distance between first and last

Possible implementation

template <class ForwardIt> void rotate(ForwardIt first, ForwardIt n_first, ForwardIt last) { ForwardIt next = n_first; while (first != next) { std::iter_swap(first++, next++); if (next == last) { next = n_first; } else if (first == n_first) { n_first = next; } } }

Example

std::rotate is a common building block in many algorithms. This example demonstrates insertion sort:

Run this code

#include <vector>
#include <iostream>
#include <algorithm>
 
int main()
{
    std::vector<int> v{2, 4, 2, 0, 5, 10, 7, 3, 7, 1}; 
 
    std::cout << "before sort:      ";
    for (int n: v)
        std::cout << n << ' ';
    std::cout << '\n';
 
    // insertion sort
    for (auto i = v.begin(); i != v.end(); ++i) {
        std::rotate(std::upper_bound(v.begin(), i, *i), i, i+1);
    }
 
    std::cout << "after sort:       ";
    for (int n: v)
        std::cout << n << ' ';
    std::cout << '\n';
 
    // simple rotation to the left
    std::rotate(v.begin(), v.begin() + 1, v.end());
 
    std::cout << "simple rotate left  : ";
    for (int n: v)
        std::cout << n << ' ';
    std::cout << '\n';
 
    // simple rotation to the right
    std::rotate(v.rbegin(), v.rbegin() + 1, v.rend());
 
    std::cout << "simple rotate right : ";
    for (int n: v)
        std::cout << n << ' ';
    std::cout << '\n';
 
}

Output:

before sort:      2 4 2 0 5 10 7 3 7 1 
after sort:       0 1 2 2 3 4 5 7 7 10 
simple rotate left : 1 2 2 3 4 5 7 7 10 0
simple rotate right: 0 1 2 2 3 4 5 7 7 10

See also

rotate_copy

copies and rotate a range of elements (function template)