std::is_permutation

equality (1)	template <class ForwardIterator1, class ForwardIterator2> bool is_permutation (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2);
predicate (2)	template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate> bool is_permutation (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, BinaryPredicate pred);

equality (1)

template <class ForwardIterator1, class ForwardIterator2>   bool is_permutation (ForwardIterator1 first1, ForwardIterator1 last1,                        ForwardIterator2 first2);

predicate (2)

template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>   bool is_permutation (ForwardIterator1 first1, ForwardIterator1 last1,                        ForwardIterator2 first2, BinaryPredicate pred);

Test whether range is permutation of another

Compares the elements in the range [first1,last1) with those in the range beginning at first2, and returns true if all of the elements in both ranges match, even in a different order.

The elements are compared using operator== (or pred, in version (2)).

The behavior of this function template is equivalent to:

template <class InputIterator1, class InputIterator2>
  bool is_permutation (InputIterator1 first1, InputIterator1 last1,
                       InputIterator2 first2)
{
  std::tie (first1,first2) = std::mismatch (first1,last1,first2);
  if (first1==last1) return true;
  InputIterator2 last2 = first2; std::advance (last2,std::distance(first1,last1));
  for (InputIterator1 it1=first1; it1!=last1; ++it1) {
    if (std::find(first1,it1,*it1)==it1) {
      auto n = std::count (first2,last2,*it1);
      if (n==0 || std::count (it1,last1,*it1)!=n) return false;
    }
  }
  return true;
}

Parameters

first1, last1: Input iterators to the initial and final positions of the first sequence. The range used is [first1,last1), which contains all the elements between first1 and last1, including the element pointed by first1 but not the element pointed by last1.
first2: Input iterator to the initial position of the second sequence.
The function considers as many elements of this sequence as those in the range [first1,last1).
If this sequence is shorter, it causes undefined behavior.
pred: Binary function that accepts two elements as argument (one of each of the two sequences, in the same order), and returns a value convertible to bool. The value returned indicates whether the elements are considered to match in the context of this function.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.

InputIterator1 and InputIterator2 shall point to the same type.

Return value

true if all the elements in the range [first1,last1) compare equal to those of the range starting at first2 in any order, and false otherwise.

Example

// is_permutation example
#include <iostream>     // std::cout
#include <algorithm>    // std::is_permutation
#include <array>        // std::array

int main () {
  std::array<int,5> foo = {1,2,3,4,5};
  std::array<int,5> bar = {3,1,4,5,2};

  if ( std::is_permutation (foo.begin(), foo.end(), bar.begin()) )
    std::cout << "foo and bar contain the same elements.\n";

  return 0;
}

Output:

foo and bar contain the same elements.

Complexity

If both sequence are equal (with the elements in the same order), linear in the distance between first1 and last1.
Otherwise, up to quadratic: Performs at most N² element comparisons until the result is determined (where N is the distance between first1 and last1).

Data races

Some (or all) of the objects in both ranges are accessed (possibly multiple times each).

Exceptions

Throws if any of the element comparisons (or pred) throws, or if any of the operations on iterators throws.
Note that invalid parameters cause undefined behavior.