prev_permutation
Permutes the order of the element
Definition
The prev_permutation() algorithm is defined in the standard header <algorithm> and in the nonstandard backward-compatibility header <algo.h>.
Interface
#include <algorithm>
template < class BidirectionalIterator >
bool prev_permutation(
BidirectionalIterator first,
BidirectionalIterator last
);
template < class BidirectionalIterator, class BinaryPredicate >
bool prev_permutation(
BidirectionalIterator first,
BidirectionalIterator last,
BinaryPredicate comp
);Parameters:
| Parameter | Description |
| first | A bidirectional iterator pointing to the position of the first element in the range to be permuted |
| last | A bidirectional iterator pointing to the position one past the final element in the range to be permuted |
| comp | User-defined predicate function object that defines the comparison criterion to be satisfied by successive elements in the ordering. A binary predicate takes two arguments and returns true when satisfied and false when not satisfied |
Description
Prev_permutation function reorders the range [first, last) into the previous permutation from the set of all permutations that are lexicographically ordered.
The first version uses operator< for comparison and the second uses the function object comp.
Return Value
Returns true if there was a previous permutation and has replaced the original ordering of the range, false otherwise.
Complexity
The complexity is linear; performs at most (last - first) / 2 swaps.
References
Example 1
The following code prints all six permutations of the string "abc" in reverse order using prev_permutation function.
#include <algorithm>
#include <string>
#include <iostream>
#include <functional>
int main()
{
std::string s="abc";
std::sort(s.begin(), s.end(), std::greater<char>());
do {
std::cout << s << ' ';
} while(std::prev_permutation(s.begin(), s.end()));
std::cout << '\n';
}Output:
cba cab bca bac acb abc