Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.
NAME
rotate, rotate_copy
- Swaps the segment that contains elements from first
through middle-1 with the segment that contains the elements
from middle through last.
SYNOPSIS
#include <algorithm>
template <class ForwardIterator>
void rotate (ForwardIterator first,
ForwardIterator middle,
ForwardIterator last);
template <class ForwardIterator, class OutputIterator>
OutputIterator rotate_copy (ForwardIterator first,
ForwardIterator middle,
ForwardIterator last,
OutputIterator result);
DESCRIPTION
The rotate algorithm takes three iterator arguments: first,
which defines the start of a sequence; last, which defines
the end of the sequence; and middle, which defines a point
within the sequence. rotate "swaps" the segment that con-
tains elements from first through middle-1 with the segment
that contains the elements from middle through last. After
rotate has been applied, the element that was in position
middle, is in position first, and the other elements in that
segment are in the same order relative to each other. Simi-
larly, the element that was in position first is now in
position last-middle +1. An example illustrates how rotate
works:
Say that we have the sequence:
2 4 6 8 1 3 5
If we call rotate with middle = 5, the two segments are
2 4 6 8 and 1 3 5
After we apply rotate, the new sequence is:
1 3 5 2 4 6 8
Note that the element that was in the fifth position is now
in the first position, and the element that was in the first
position is in position 4 (last - first + 1, or 8 - 5 +1
=4).
The formal description of this algorithms is: for each non-
negative integer i < (last - first), rotate places the ele-
ment from the position first + i into position first + (i +
(last - middle)) % (last - first). [first, middle) and [mid-
dle, last) are valid ranges.
rotate_copy rotates the elements as described above, but
instead of swapping elements within the same sequence, it
copies the result of the rotation to a container specified
by result. rotate_copy copies the range [first, last) to the
range [result, result + (last - first)) such that for each
non- negative integer i < (last - first) the following
assignment takes place:
*(result + (i + (last - middle)) % (last -first)) = *(first
+ i).
The ranges [first, last) and [result, result, + (last -
first)) may not overlap.
COMPLEXITY
For rotate, at most last - first swaps are performed.
For rotate_copy, last - first assignments are performed.
EXAMPLE
//
// rotate
//
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
int main()
{
//Initialize a vector with an array of ints
int arr[10] = {1,2,3,4,5,6,7,8,9,10};
vector<int> v(arr, arr+10);
//Print out elements in original (sorted) order
cout << "Elements before rotate: " << endl << " ";
copy(v.begin(),v.end(),
ostream_iterator<int,char>(cout," "));
cout << endl << endl;
//Rotate the elements
rotate(v.begin(), v.begin()+4, v.end());
//Print out the rotated elements
cout << "Elements after rotate: " << endl << " ";
copy(v.begin(),v.end(),
ostream_iterator<int,char>(cout," "));
cout << endl;
return 0;
}
Program Output
Elements before rotate:
1 2 3 4 5 6 7 8 9 10
Elements after rotate:
5 6 7 8 9 10 1 2 3 4
WARNINGS
If your compiler does not support default template parame-
ters, then you always need to supply the Allocator template
argument. For instance, you need to write:
vector<int, allocator<int> >
instead of:
vector<int>
If your compiler does not support namespaces, then you do
not need the using declaration for std.