C++ Algorithm Library - is_permutation() Function


The C++ function std::algorithm::is_permutation() tests whether a sequence is permutation of other or not. It uses binary predicate for comparison.


Following is the declaration for std::algorithm::is_permutation() function form std::algorithm header.


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


  • first1 − Input iterator to the initial position of the first sequence.

  • last1 − Input iterator to the final position of the first sequence.

  • first2 − Input iterator to the initial position of the second sequence.

  • pred − A binary predicate which accepts two arguments and returns bool.

Return value

Returns true if first range is permutation of another otherwise it returns false.


Throws exception if either the binary predicate or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

Time complexity



The following example shows the usage of std::algorithm::is_permutation() function.

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

bool ignore_case(char a, char b) {
   return (tolower(a) == tolower(b));

int main(void) {
   vector<char> v1 = {'A', 'B', 'C', 'D', 'E'};
   vector<char> v2 = {'a', 'b', 'c', 'd', 'e'};
   bool result;

   result = is_permutation(v1.begin(), v1.end(), v2.begin());

   if (result == false)
      cout << "Both vector doesn't contain same elements." << endl;

   result = is_permutation(v1.begin(), v1.end(), v2.begin(), ignore_case);

   if (result == true)
      cout << "Both vector contains same elements." << endl;

   return 0;

Let us compile and run the above program, this will produce the following result −

Both vector doesn't contain same elements.
Both vector contains same elements.