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std::rotate

From cppreference.com
< cpp‎ | algorithm
 
 
 

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.

Contents

[edit] 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.

[edit] Return value

(none)

(until C++11)

The iterator equal to first + (last - n_first)

(since C++11)

[edit] Complexity

Linear in the distance between first and last

[edit] 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;
        }
    }
}

[edit] Example

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

#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

[edit] See also

copies and rotate a range of elements
(function template) [edit]