< cpp‎ | algorithm
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations

Numeric operations
Operations on uninitialized storage
C library
Defined in header <algorithm>
template< class BidirIt >
          bool next_permutation( BidirIt first, BidirIt last );
(until C++20)
template< class BidirIt >
constexpr bool next_permutation( BidirIt first, BidirIt last );
(since C++20)
template< class BidirIt, class Compare >
          bool next_permutation( BidirIt first, BidirIt last, Compare comp );
(until C++20)
template< class BidirIt, class Compare >
constexpr bool next_permutation( BidirIt first, BidirIt last, Compare comp );
(since C++20)

Permutes the range [firstlast) into the next permutation, where the set of all permutations is ordered lexicographically with respect to operator< or comp. Returns true if such a "next permutation" exists; otherwise transforms the range into the lexicographically first permutation (as if by std::sort(first, last, comp)) and returns false.


[edit] Parameters

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);

While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1& is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy (since C++11)).
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 LegacyBidirectionalIterator.

[edit] Return value

true if the new permutation is lexicographically greater than the old. false if the last permutation was reached and the range was reset to the first permutation.

[edit] Exceptions

Any exceptions thrown from iterator operations or the element swap.

[edit] Complexity

At most N/2 swaps, where N = std::distance(first, last). Averaged over the entire sequence of permutations, typical implementations use about 3 comparisons and 1.5 swaps per call.

[edit] Notes

Implementations (e.g. MSVC STL) may enable vectorization when the iterator type satisfies LegacyContiguousIterator and swapping its value type calls neither non-trivial special member function nor ADL-found swap.

[edit] Possible implementation

template<class BidirIt>
bool next_permutation(BidirIt first, BidirIt last)
    auto r_first = std::make_reverse_iterator(last);
    auto r_last = std::make_reverse_iterator(first);
    auto left = std::is_sorted_until(r_first, r_last);
    if (left != r_last)
        auto right = std::upper_bound(r_first, left, *left);
        std::iter_swap(left, right);
    std::reverse(left.base(), last);
    return left != r_last;

[edit] Example

The following code prints all three permutations of the string "aba".

#include <algorithm>
#include <iostream>
#include <string>
int main()
    std::string s = "aba";
    do std::cout << s << '\n';
    while (std::next_permutation(s.begin(), s.end()));
    std::cout << s << '\n';



[edit] 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]
generates the next greater lexicographic permutation of a range of elements
(niebloid) [edit]