# Lexicographically largest sub-sequence of the given string

Given a string str containing lowercase characters, the task is to find the lexicographically largest sub-sequence of str.

Examples:

Input: str = “abc”
Output: c
All possible sub-sequences are “a”, “ab”, “ac”, “b”, “bc” and “c”
and “c” is the largest among them (lexicographically)

Input: str = “geeksforgeeks”
Output: ss

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Let mx be the lexicographically largest character in the string. Since we want the lexicographically largest sub-sequence we should include all occurrences of mx. Now after all the occurrences have been used, the same process can be repeated for the remaining string (i.e. sub-string after the last occurrence of mx) and so on until the there are no more characters left.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function to return the lexicographically ` `// largest sub-sequence of s ` `string getSubSeq(string s, ``int` `n) ` `{ ` `    ``string res = ``""``; ` `    ``int` `cr = 0; ` `    ``while` `(cr < n) { ` ` `  `        ``// Get the max character from the string ` `        ``char` `mx = s[cr]; ` `        ``for` `(``int` `i = cr + 1; i < n; i++) ` `            ``mx = max(mx, s[i]); ` `        ``int` `lst = cr; ` ` `  `        ``// Use all the occurrences of the ` `        ``// current maximum character ` `        ``for` `(``int` `i = cr; i < n; i++) ` `            ``if` `(s[i] == mx) { ` `                ``res += s[i]; ` `                ``lst = i; ` `            ``} ` ` `  `        ``// Repeat the steps for the remaining string ` `        ``cr = lst + 1; ` `    ``} ` `    ``return` `res; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``string s = ``"geeksforgeeks"``; ` `    ``int` `n = s.length(); ` `    ``cout << getSubSeq(s, n); ` `} `

## Java

 `// Java implementation of the approach ` `class` `GFG ` `{ ` ` `  `    ``// Function to return the lexicographically ` `    ``// largest sub-sequence of s ` `    ``static` `String getSubSeq(String s, ``int` `n) ` `    ``{ ` `        ``String res = ``""``; ` `        ``int` `cr = ``0``; ` `        ``while` `(cr < n)  ` `        ``{ ` ` `  `            ``// Get the max character from the String ` `            ``char` `mx = s.charAt(cr); ` `            ``for` `(``int` `i = cr + ``1``; i < n; i++) ` `            ``{ ` `                ``mx = (``char``) Math.max(mx, s.charAt(i)); ` `            ``} ` `            ``int` `lst = cr; ` ` `  `            ``// Use all the occurrences of the ` `            ``// current maximum character ` `            ``for` `(``int` `i = cr; i < n; i++)  ` `            ``{ ` `                ``if` `(s.charAt(i) == mx)  ` `                ``{ ` `                    ``res += s.charAt(i); ` `                    ``lst = i; ` `                ``} ` `            ``} ` ` `  `            ``// Repeat the steps for  ` `            ``// the remaining String ` `            ``cr = lst + ``1``; ` `        ``} ` `        ``return` `res; ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `main(String[] args)  ` `    ``{ ` `        ``String s = ``"geeksforgeeks"``; ` `        ``int` `n = s.length(); ` `        ``System.out.println(getSubSeq(s, n)); ` `    ``} ` `} ` ` `  `// This code is contributed by Rajput-Ji `

## Python3

 `# Python 3 implementation of the approach ` ` `  `# Function to return the lexicographically ` `# largest sub-sequence of s ` `def` `getSubSeq(s, n): ` `    ``res ``=` `"" ` `    ``cr ``=` `0` `    ``while` `(cr < n): ` `         `  `        ``# Get the max character from  ` `        ``# the string ` `        ``mx ``=` `s[cr] ` `        ``for` `i ``in` `range``(cr ``+` `1``, n): ` `            ``mx ``=` `max``(mx, s[i]) ` `        ``lst ``=` `cr ` ` `  `        ``# Use all the occurrences of the ` `        ``# current maximum character ` `        ``for` `i ``in` `range``(cr,n): ` `            ``if` `(s[i] ``=``=` `mx): ` `                ``res ``+``=` `s[i] ` `                ``lst ``=` `i ` ` `  `        ``# Repeat the steps for the  ` `        ``# remaining string ` `        ``cr ``=` `lst ``+` `1` `     `  `    ``return` `res ` ` `  `# Driver code ` `if` `__name__ ``=``=` `'__main__'``: ` `    ``s ``=` `"geeksforgeeks"` `    ``n ``=` `len``(s) ` `    ``print``(getSubSeq(s, n)) ` ` `  `# This code is contributed by ` `# Surendra_Gangwar `

## C#

 `// C# implementation of the approach  ` `using` `System; ` ` `  `class` `GFG  ` `{  ` ` `  `    ``// Function to return the lexicographically  ` `    ``// largest sub-sequence of s  ` `    ``static` `String getSubSeq(String s, ``int` `n)  ` `    ``{  ` `        ``String res = ``""``;  ` `        ``int` `cr = 0;  ` `        ``while` `(cr < n)  ` `        ``{  ` ` `  `            ``// Get the max character from  ` `            ``// the String  ` `            ``char` `mx = s[cr];  ` `            ``for` `(``int` `i = cr + 1; i < n; i++)  ` `            ``{  ` `                ``mx = (``char``) Math.Max(mx, s[i]);  ` `            ``}  ` `            ``int` `lst = cr;  ` ` `  `            ``// Use all the occurrences of the  ` `            ``// current maximum character  ` `            ``for` `(``int` `i = cr; i < n; i++)  ` `            ``{  ` `                ``if` `(s[i] == mx)  ` `                ``{  ` `                    ``res += s[i];  ` `                    ``lst = i;  ` `                ``}  ` `            ``}  ` ` `  `            ``// Repeat the steps for  ` `            ``// the remaining String  ` `            ``cr = lst + 1;  ` `        ``}  ` `        ``return` `res;  ` `    ``}  ` ` `  `    ``// Driver code  ` `    ``public` `static` `void` `Main(String[] args)  ` `    ``{  ` `        ``String s = ``"geeksforgeeks"``;  ` `        ``int` `n = s.Length;  ` `        ``Console.WriteLine(getSubSeq(s, n));  ` `    ``}  ` `}  ` ` `  `// This code is contributed by 29AjayKumar `

## PHP

 ` `

Output:

```ss
```

Time Complexity: O(N) where N is the length of the string.

My Personal Notes arrow_drop_up Check out this Author's contributed articles.

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.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Article Tags :
Practice Tags :

1

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.