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# Find the longest common prefix between two strings after performing swaps on second string

• Last Updated : 21 May, 2021

Given two strings and . Find the longest common prefix between them after performing zero or more operations on string . In each operation, you can swap any two letters.
Examples

```Input : a = "here", b = "there"
Output : 4
The 2nd string can be made "heret" by just
swapping characters and thus the longest
prefix is of length 4.

Input : a = "you", b = "me"
Output : 0```

Given that we are only allowed to performs swaps in the string and the length of prefix should be maximized. So the idea is to traverse string and check if the frequency of current character in string is same or less of that in string . If yes then move forward in string an otherwise break and print the length of the part of string an up to which a character is matched in string .
Below is the implementation of the above approach:

## C++

 `// C++ program to find the longest``// common prefix between two strings``// after performing swaps on the second string``#include ``using` `namespace` `std;` ` ` `void` `LengthLCP(string x, string y)``{``    `  `    ``int` `fr={0};``     ` `    ``int` `a = x.length(); ``// length of x``    ``int` `b = y.length(); ``// length of y``     ` `    ``for` `(``int` `i=0 ;i 0){``            ``c += 1;``            ``fr[x[i] - 97] -= 1;``        ``}``        ``else``            ``break``;``    ``}``    ``cout<<(c)<

## Java

 `// Java program to find the longest``// common prefix between two strings``// after performing swaps on the second string` `public` `class` `GFG {` `    ``static` `void` `LengthLCP(String x, String y)``    ``{``        `  `        ``int` `fr[]=``new` `int` `[``26``];``         ` `        ``int` `a = x.length(); ``// length of x``        ``int` `b = y.length(); ``// length of y``         ` `        ``for` `(``int` `i=``0` `;i ``0``){``                ``c += ``1``;``                ``fr[x.charAt(i) - ``97``] -= ``1``;``            ``}``            ``else``                ``break``;``        ``}``        ``System.out.println((c)) ;``    ``}`  `    ``public` `static` `void` `main(String args[])``    ``{``        ``String x=``"here"``, y =  ``"there"``;``         ` `        ``LengthLCP(x, y);`  `    ``}``    ``// This code is contributed by ANKITRAI1``}`` `

## Python3

 `# Python program to find the longest``# common prefix between two strings``# after performing swaps on the second string` `def` `LengthLCP(x, y):``    ``fr ``=` `[``0``] ``*` `26``    ` `    ``a ``=` `len``(x) ``# length of x``    ``b ``=` `len``(y) ``# length of y``    ` `    ``for` `i ``in` `range``(b):``        ``# creating frequency array of``        ``# characters of y``        ``fr[``ord``(y[i]) ``-` `97``] ``+``=` `1``    ` `    ``# storing the length of``    ``# longest common prefix``    ``c ``=` `0``    ` `    ``for` `i ``in` `range``(a):``        ``# checking if the frequency of the character at``        ``# position i in x in b is greater than zero or not``        ``# if zero we increase the prefix count by 1``        ``if` `(fr[``ord``(x[i]) ``-` `97``] > ``0``):``            ``c ``+``=` `1``            ``fr[``ord``(x[i]) ``-` `97``] ``-``=` `1``        ``else``:``            ``break``    ``print``(c)` `# Driver Code` `x, y ``=` `"here"``, ``"there"` `LengthLCP(x, y)`

## C#

 `// C# program to find the longest``// common prefix between two strings``// after performing swaps on the``// second string``using` `System;` `class` `GFG``{` `static` `void` `LengthLCP(String x, String y)``{``    ``int` `[]fr = ``new` `int` `;``    ` `    ``int` `a = x.Length; ``// length of x``    ``int` `b = y.Length; ``// length of y``    ` `    ``for` `(``int` `i = 0 ; i < b; i++)``    ``{``        ``// creating frequency array``        ``// of characters of y``        ``fr[y[i] - 97] += 1;``    ``}``    ` `    ``// storing the length of``    ``// longest common prefix``    ``int` `c = 0;``    ` `    ``for` `(``int` `i = 0 ; i < a; i++)``    ``{``        ``// checking if the frequency of``        ``// the character at position i``        ``// in x in b is greater than zero``        ``// or not if zero we increase the``        ``// prefix count by 1``        ``if` `(fr[x[i] - 97] > 0)``        ``{``            ``c += 1;``            ``fr[x[i] - 97] -= 1;``        ``}``        ``else``            ``break``;``    ``}``    ``Console.Write((c)) ;``}` `// Driver Code``public` `static` `void` `Main()``{``    ``String x = ``"here"``, y = ``"there"``;``    ` `    ``LengthLCP(x, y);``}``}` `// This code is contributed by 29AjayKumar`

## PHP

 ` 0)``        ``{``            ``\$c` `+= 1;``            ``\$fr``[ord(``\$x``[``\$i``]) - 97] -= 1;``        ``}``        ``else``            ``break``;``    ``}``    ``echo` `\$c``;``}` `// Driver Code``\$x``=``"here"``;``\$y` `= ``"there"``;` `LengthLCP(``\$x``, ``\$y``);` `return` `0;` `// This code is contributed by ChitraNayal``?>`

## Javascript

 ``
Output:
`4`

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