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# //

Permutes the order of the element
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## 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:

##### Example - prev_permutation algorithm
Problem
The following code prints all six permutations of the string "abc" in reverse order using prev_permutation function.
Workings
```#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';
}```
Solution
Output:

cba cab bca bac acb abc
References