std::is_permutation
From Cppreference
| Defined in header <algorithm>
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| template< class ForwardIterator1, class ForwardIterator2 >
bool is_permutation( ForwardIterator1 first, ForwardIterator1 last, |
(1) | (C++11 feature) |
| template< class ForwardIterator1, class ForwardIterator2, class BinaryPredicate >
bool is_permutation( ForwardIterator1 first, ForwardIterator1 last, |
(2) | (C++11 feature) |
Returns true if there exists a permutation of the elements in the range [first1, last1) that makes that range equal to the range beginning at d_first. The first version uses operator== for equality, the second version uses the binary predicate p
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[edit] Parameters
| first, last | - | the range of elements to compare | |||||||||
| d_first | - | the beginning of the second range to compare | |||||||||
| p | - | binary predicate which returns true if the elements should be treated as equal. The signature of the predicate function should be equivalent to the following:
The signature does not need to have const &, but the function must not modify the objects passed to it. |
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[edit] Return value
true if the range [first, last) is a permutation of the range beginning at d_first.
[edit] Complexity
At most O(N2) applications of the predicate, or exactly N if the sequences are already equal, where N=std::distance(first, last).
[edit] Equivalent function
template<class ForwardIterator1, class ForwardIterator2> bool is_permutation(ForwardIterator1 first, ForwardIterator1 last, ForwardIterator2 d_first) { // skip common prefix std::tie(first, d_first) = std::mismatch(first, last, d_first); // iterate over the rest, counting how many times each element // from [first, last) appears in [d_first, d_last) if (first != last) { ForwardIterator2 d_last = d_first; std::advance(d_last, std::distance(first, last)); for (ForwardIterator1 i = first; i != last; ++i) { if (i != std::find(first, i, *i)) continue; // already counted this *i auto m = std::count(d_first, d_last, *i); if (m==0 || std::count(i, last, *i) != m) { return false; } } } return true; } |
[edit] Example
#include <algorithm> #include <vector> #include <iostream> int main() { std::vector<int> v1{1,2,3,4,5}; std::vector<int> v2{3,5,4,1,2}; std::cout << "3,5,4,1,2 is a permutation of 1,2,3,4,5? " << std::boolalpha << std::is_permutation(v1.begin(), v1.end(), v2.begin()) << '\n'; std::vector<int> v3{3,5,4,1,1}; std::cout << "3,5,4,1,1 is a permutation of 1,2,3,4,5? " << std::boolalpha << std::is_permutation(v1.begin(), v1.end(), v3.begin()) << '\n'; }
Output:
3,5,4,1,2 is a permutation of 1,2,3,4,5? true 3,5,4,1,1 is a permutation of 1,2,3,4,5? false
[edit] See also
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generates the next greater lexicographic permutation of a range of elements (function template) |
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generates the next smaller lexicographic permutation of a range of elements (function template) |
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