# Find the lexicographically largest palindromic Subsequence of a String

• Difficulty Level : Easy
• Last Updated : 02 Aug, 2021

Given a string . The task is to find the lexicographically largest subsequence of the string which is a palindrome.
Examples:

```Input : str = "abrakadabra"
Output : rr

Input : str = "geeksforgeeks"
Output : ss```

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The idea is to observe a character a is said to be lexicographically larger than a character b if it’s ASCII value is greater than that of b.
Since the string has to be palindromic, the string should contain the largest characters only, as if we place any other smaller character in between the first and last character then it will make the string lexicographically smaller.
To find the lexicographically largest subsequence, first find the largest characters in the given string and append all of its occurrences in the original string to form the resultant subsequence string.
Below is the implementation of the above approach:

## C++

 `// CPP program to find the largest``// palindromic subsequence` `#include ``using` `namespace` `std;` `// Function to find the largest``// palindromic subsequence``string largestPalinSub(string s)``{``    ``string res;` `    ``char` `mx = s;` `    ``// Find the largest character``    ``for` `(``int` `i = 1; i < s.length(); i++)``        ``mx = max(mx, s[i]);` `    ``// Append all occurrences of largest character``    ``// to the resultant string``    ``for` `(``int` `i = 0; i < s.length(); i++)``        ``if` `(s[i] == mx)``            ``res += s[i];` `    ``return` `res;``}` `// Driver Code``int` `main()``{``    ``string s = ``"geeksforgeeks"``;` `    ``cout << largestPalinSub(s);``}`

## Java

 `// Java program to find the largest``// palindromic subsequence``class` `GFG``{` `// Function to find the largest``// palindromic subsequence``static` `String largestPalinSub(String s)``{``    ``String res = ``""``;``    ``char` `mx = s.charAt(``0``);` `    ``// Find the largest character``    ``for` `(``int` `i = ``1``; i < s.length(); i++)``        ``mx = (``char``)Math.max((``int``)mx,``                  ``(``int``)s.charAt(i));` `    ``// Append all occurrences of largest``    ``// character to the resultant string``    ``for` `(``int` `i = ``0``; i < s.length(); i++)``        ``if` `(s.charAt(i) == mx)``            ``res += s.charAt(i);` `    ``return` `res;``}` `// Driver Code``public` `static` `void` `main(String []args)``{``    ``String s = ``"geeksforgeeks"``;``    ``System.out.println(largestPalinSub(s));``}``}` `// This code is contributed by``// Rituraj Jain`

## Python3

 `# Python3 program to find the largest``# palindromic subsequence` `# Function to find the largest``# palindromic subsequence``def` `largestPalinSub(s):` `    ``res ``=` `""``    ``mx ``=` `s[``0``]` `    ``# Find the largest character``    ``for` `i ``in` `range``(``1``, ``len``(s)):``        ``mx ``=` `max``(mx, s[i])` `    ``# Append all occurrences of largest``    ``# character to the resultant string``    ``for` `i ``in` `range``(``0``, ``len``(s)):``        ``if` `s[i] ``=``=` `mx:``            ``res ``+``=` `s[i]` `    ``return` `res` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:` `    ``s ``=` `"geeksforgeeks"``    ``print``(largestPalinSub(s))` `# This code is contributed by``# Rituraj Jain`

## C#

 `// C# program to find the largest``// palindromic subsequence``using` `System;` `class` `GFG``{` `    ``// Function to find the largest``    ``// palindromic subsequence``    ``static` `string` `largestPalinSub(``string` `s)``    ``{``        ``string` `res = ``""``;``        ``char` `mx = s;``    ` `        ``// Find the largest character``        ``for` `(``int` `i = 1; i < s.Length; i++)``            ``mx = (``char``)Math.Max((``int``)mx,``                    ``(``int``)s[i]);``    ` `        ``// Append all occurrences of largest``        ``// character to the resultant string``        ``for` `(``int` `i = 0; i < s.Length; i++)``            ``if` `(s[i] == mx)``                ``res += s[i];``    ` `        ``return` `res;``    ``}``    ` `    ``// Driver Code``    ``public` `static` `void` `Main()``    ``{``        ``string` `s = ``"geeksforgeeks"``;``        ``Console.WriteLine(largestPalinSub(s));``    ``}``}` `// This code is contributed by Ryuga`

## PHP

 ``

## Javascript

 ``
Output:
`ss`

Time Complexity: O(N), where N is the length of the string.
Auxiliary Space: O(1)

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