< cpp‎ | algorithm
Revision as of 21:45, 31 May 2013 by P12bot (Talk | contribs)

Defined in header <algorithm>
template< class BidirIt >
bool prev_permutation( BidirIt first, BidirIt last);
template< class BidirIt, class Compare >
bool prev_permutation( BidirIt first, BidirIt last, Compare comp);

Transforms the range [first, last) into the previous permutation from the set of all permutations that are lexicographically ordered with respect to operator< or comp. Returns true if such permutation exists, otherwise transforms the range into the last permutation (as if by std::sort(first, last); std::reverse(first, last);) and returns false.



first, last - the range of elements to permute
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than the second.

The signature of the comparison function should be equivalent to the following:

 bool cmp(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function object must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type BidirIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
BidirIt must meet the requirements of ValueSwappable and BidirectionalIterator.

Return value

true if the new permutation precedes the old in lexicographical order. false if the first permutation was reached and the range was reset to the last permutation.


Any exceptions thrown from iterator operations or the element swap.


At most (last-first)/2 swaps.

Possible implementation

template<class BidirIt>
bool prev_permutation(BidirIt first, BidirIt last)
    if (first == last) return false;
    BidirIt i = last;
    if (first == --i) return false;
    while (1) {
        BidirIt i1, i2;
        i1 = i;
        if (*i1 < *--i) {
            i2 = last;
            while (!(*--i2 < *i))
            std::iter_swap(i, i2);
            std::reverse(i1, last);
            return true;
        if (i == first) {
            std::reverse(first, last);
            return false;


The following code prints all six permutations of the string "abc" in reverse order

#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';


cba cab bca bac acb abc

See also

determines if a sequence is a permutation of another sequence
(function template) [edit]
generates the next smaller lexicographic permutation of a range of elements
(function template) [edit]