# is_permutation() in C++ and its application for anagram search

• Difficulty Level : Medium
• Last Updated : 16 Nov, 2021

is_permutations() is used to check if two containers like string and vector are permutation of each other. It accepts three parameters, the first two parameters are begin and end positions of first object and third parameter begin position of second object.

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## CPP

 `// C++ program to demonstrate working of``// is_permutation()``#include ``using` `namespace` `std;` `// Driver program to test above``int` `main()``{``    ``vector<``int``> v1{1, 2, 3, 4};``    ``vector<``int``> v2{2, 3, 1, 4};` `    ``// v1 and v2 are permutation of each other``    ``if` `(is_permutation(v1.begin(), v1.end(), v2.begin()))``        ``cout << ``"True\n"``;``    ``else``        ``cout << ``"False\n"``;` `    ``// v1 and v3 are NOT permutation of each other``    ``vector<``int``> v3{5, 3, 1, 4};``    ``if` `(is_permutation(v1.begin(), v1.end(), v3.begin()))``        ``cout << ``"True\n"``;``    ``else``        ``cout << ``"False\n"``;` `    ``return` `0;``}`

Output :

```True
False```

Application :
Given a pattern and a text, find all occurrences of pattern and its anagrams in text.
Examples:

```Input : text ="forxxorfxdofr"
pat = "for"
Output :  3
There are three anagrams of "for"
int text.

Input : word = "aabaabaa"
text = "aaba"
Output : 4```

We have discussed a (n) solution her. But in this post it is done using is_permutation(). Although the complexity is higher than previously discussed method, but the purpose is to explain application of is_permutation().
Let size of pattern to be searched be pat_len. The idea is to traverse given text and for every window of size pat_len, check if it is a permutation of given pattern or not.

## CPP

 `// C++ program to count all permutation of``// given text``#include``using` `namespace` `std;` `// Function to count occurrences of anagrams of pat``int` `countAnagrams(string text, string pat)``{``    ``int` `t_len = text.length();``    ``int` `p_len = pat.length();` `    ``// Start traversing the text``    ``int` `count = 0; ``// Initialize result``    ``for` `(``int` `i=0; i<=t_len-p_len; i++)` `        ``// Check if substring text[i..i+p_len]``        ``// is a permutation of pat[].``        ``// Three parameters are :``        ``// 1) Beginning position of current window in text``        ``// 2) End position of current window in text``        ``// 3) Pattern to be matched with current window``        ``if` `(is_permutation(text.begin()+i,``                           ``text.begin()+i+p_len,``                           ``pat.begin()))``            ``count++;` `    ``return` `count;``}` `// Driver code``int` `main()``{``    ``string str = ``"forxxorfxdofr"``;``    ``string pat = ``"for"``;``    ``cout << countAnagrams(str, pat) << endl;``    ``return` `0;``}`

Output:

`3`

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