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# Lexicographic rank of a string using STL

You are given a string, find its rank among all its permutations sorted lexicographically.

Examples:

```Input : str[] = "acb"
Output : Rank = 2

Input : str[] = "string"
Output : Rank = 598

Input : str[] = "cba"
Output : Rank = 6```

We have already discussed solutions to find Lexicographic rank of string In this post, we use the STL function “next_permutation ()” to generate all possible permutations of the given string and, as it gives us permutations in lexicographic order, we will put an iterator to find the rank of each string. While iterating when Our permuted string becomes identical to the original input string, we break from the loop and the iterator value for the last iteration is our required result.

Implementation:

## C++

 `// C++ program to print rank of``// string using next_permute()``#include ``using` `namespace` `std;` `// Function to print rank of string``// using next_permute()``int` `findRank(string str)``{``    ``// store original string``    ``string orgStr = str;` `    ``// Sort the string in lexicographically``    ``// ascending order``    ``sort(str.begin(), str.end());` `    ``// Keep iterating until``    ``// we reach equality condition``    ``long` `int` `i = 1;``    ``do` `{``        ``// check for nth iteration``        ``if` `(str == orgStr)``            ``break``;` `        ``i++;``    ``} ``while` `(next_permutation(str.begin(), str.end()));` `    ``// return iterator value``    ``return` `i;``}` `// Driver code``int` `main()``{``    ``string str = ``"cba"``;``    ``cout << findRank(str);``    ``return` `0;``}`

## Python3

 `# Python program to print rank of``# string using itertools.permutations``import` `itertools` `# Function to print rank of string``# using itertools.permutations``def` `findRank(``str``):``    ``# Store original string and``    ` `    ``# Sort the string in lexicographically``    ``# ascending order``    ``orgStr ``=` `''.join(``sorted``(``str``))``    ` `    ``# Create an dictionary to handle``    ``# repeating characters in Python``    ``# while using itertools.permutations``    ``d``=``[]` `    ``# Keep iterating until we reach equality condition``    ``i ``=` `1``    ``for` `permutation ``in` `itertools.permutations(orgStr):``        ``if` `permutation ``not` `in` `d:``            ``d.append(permutation)``            ``# check for nth iteration``            ``if` `''.join(permutation) ``=``=` `str``:``                ``break``            ``i ``+``=` `1` `    ``# Return iterator value``    ``return` `i` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``str` `=` `'bca'``    ``print``(findRank(``str``))``    ` `# This code is contributed by Utkarsh.`

## C#

 `using` `System;``using` `System.Collections.Generic;``using` `System.Linq;` `class` `Program``{``    ``// Function to print rank of string``    ``// using itertools.permutations``    ``static` `int` `FindRank(``string` `str)``    ``{``        ``// Store original string and` `        ``// Sort the string in lexicographically``        ``// ascending order``        ``string` `orgStr = ``new` `string``(str.OrderBy(c => c).ToArray());` `        ``// Create a set to handle``        ``// repeating characters in C#``        ``// while using itertools.permutations``        ``HashSet<``string``> ``set` `= ``new` `HashSet<``string``>();` `        ``// Keep iterating until we reach equality condition``        ``int` `i = 1;``        ``foreach` `(``var` `permutation ``in` `Permutations(orgStr))``        ``{``            ``if` `(!``set``.Contains(permutation))``            ``{``                ``set``.Add(permutation);``                ``// check for nth iteration``                ``if` `(permutation == str)``                ``{``                    ``break``;``                ``}``                ``i++;``            ``}``        ``}` `        ``// Return iterator value``        ``return` `i;``    ``}` `    ``// Function to get all permutations of a string``    ``static` `IEnumerable<``string``> Permutations(``string` `str)``    ``{``        ``if` `(str.Length == 1)``        ``{``            ``yield` `return` `str;``        ``}``        ``else``        ``{``            ``foreach` `(``var` `ch ``in` `str)``            ``{``                ``foreach` `(``var` `permutation ``in` `Permutations(str.Remove(str.IndexOf(ch), 1)))``                ``{``                    ``yield` `return` `ch + permutation;``                ``}``            ``}``        ``}``    ``}` `    ``// Driver code``    ``static` `void` `Main(``string``[] args)``    ``{``        ``string` `str = ``"bca"``;``        ``Console.WriteLine(FindRank(str));``    ``}``}`  `// This code is contributed by shiv1o43g`

Output

`6`

Time Complexity: O(n log n)
Auxiliary Space: O(1)

This article is contributed by Aarti_Rathi and Shivam Pradhan (anuj_charm). If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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