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std::is_permutation in C++ STL

  • Difficulty Level : Medium
  • Last Updated : 06 Jul, 2017

The C++ function std::algorithm::is_permutation() tests whether a sequence is permutation of other or not. It uses operator == for comparison. This function was defined in C++11.
Syntax:

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

first1, last1: Input iterators to the initial 
and final positions of the first sequence.
first2 : Input iterator to the initial position of the second sequence. 

Return value :
true : if all the elements in range [first1, last1] 
compare equal to those of the range
starting at first2 in any order.
false : Any element missing or exceeding.

The function considers as many elements of this sequence as those in the range [first1, last1]. If this sequence is shorter, it causes undefined behaviour.




// CPP program to check if 
// two arrays are equal or not
// using std :: is_permutation
#include <iostream>
#include <algorithm>
  
//Driver Code
int main()
{
    int A[] = {1, 7, 0, 2};
    int B[] = {0, 7, 2, 1};
      
    // Check if array B includes all elements of 
    // array A
    if ( std :: is_permutation ( A, A+4, B ) )
    {
        std :: cout << "B is a permutation of A" ;
    }
      
    else
    {
        std :: cout << "B is not a permutation of A" ;
    }
    return 0;
}

Output:

B is a permutation of A

Other approach to find if arrays are equal or not is discussed here .

Another Example: Check whether two strings are anagram of each other






// CPP program to check whether two strings 
// are anagram of each other
// using std :: is_permutation
#include <iostream>
#include <algorithm>
  
/*Driver Code*/
int main()
{
    std :: string A = "SILENT";
    std :: string B = "LISTEN";
      
    /*Checking if B is a permutation of A*/
    if ( is_permutation ( A.begin(), A.end(), B.begin() ) )
    {
        std :: cout << "Anagrams" ;
    }
      
    else
    {
        std :: cout << "Not Anagrams" ;
    }
    return 0;
}

Output:

Anagrams

Other approach to Check whether two strings are anagram of each other is discussed here .

Versions of std::permutation

template< class ForwardIt1, class ForwardIt2 >
bool is_permutation( ForwardIt1 first1, ForwardIt1 last1,
                     ForwardIt2 first2 );
// (since C++11)
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate >
bool is_permutation( ForwardIt1 first1, ForwardIt1 last1,
                     ForwardIt2 first2, BinaryPredicate p );
// (since C++11)
template< class ForwardIt1, class ForwardIt2 >
bool is_permutation( ForwardIt1 first1, ForwardIt1 last1,
                     ForwardIt2 first2, ForwardIt2 last2 );
// (since C++14)
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate >
bool is_permutation( ForwardIt1 first1, ForwardIt1 last1,
                     ForwardIt2 first2, ForwardIt2 last)2,
                     BinaryPredicate p );
//(since C++14)

first1, last1 : the range of elements to compare
first2, last2 : the second range to compare
p : binary predicate which returns ​true if the elements should be treated as equal.

Examples:




// False
is_permutation ( c1.begin(),     c1.end (), c2.begin(), c2.end ()) 
  
// True
is_permutation ( c1.begin() + 1, c1.end (), c2.begin(), c2.end ())
  
// True, all empty ranges are permutations of each other
is_permutation ( c1.end (), c1.end (), c2.end(), c2.end ())

Reference : Official C++ Documentation for std :: is_permutation

This article is contributed by Rohit Thapliyal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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