std::next_permutation
<algorithm>
bool next_permutation( BidirIt first, BidirIt last );
bool next_permutation( BidirIt first, BidirIt last, Compare comp );
Permutes the range [first, last) into the next permutation. Returns true if such a "next permutation" exists; otherwise transforms the range into the lexicographically first permutation (as if by std::sort ) and returns false.
If the type of *first is not Swappable (until C++11)BidirIt is not ValueSwappable (since C++11), the behavior is undefined.
Contents
[edit] Parameters
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.
BidirIt must meet the requirements of 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] Complexity
Given \(\scriptsize N\)N as std::distance (first, last):
[edit] Exceptions
Any exceptions thrown from iterator operations or the element 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] Notes
Averaged over the entire sequence of permutations, typical implementations use about 3 comparisons and 1.5 swaps per call.
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] 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'; }
Output:
aba baa aab
[edit] See also
(function template) [edit]
(algorithm function object)[edit]