# 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

**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 <bits/stdc++.h>` `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

`<?php` `// PHP implementation of the approach` `// Function to return the lexicographically` `// largest sub-sequence of s` `function` `getSubSeq(` `$s` `, ` `$n` `)` `{` ` ` `$res` `= ` `""` `;` ` ` `$cr` `= 0;` ` ` `while` `(` `$cr` `< ` `$n` `)` ` ` `{` ` ` `// Get the max character from the string` ` ` `$mx` `= ` `$s` `[` `$cr` `];` ` ` `for` `(` `$i` `= ` `$cr` `+ 1; ` `$i` `< ` `$n` `; ` `$i` `++)` ` ` `$mx` `= max(` `$mx` `, ` `$s` `[` `$i` `]);` ` ` `$lst` `= ` `$cr` `;` ` ` `// Use all the occurrences of the` ` ` `// current maximum character` ` ` `for` `(` `$i` `= ` `$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` `$s` `= ` `"geeksforgeeks"` `;` `$n` `= ` `strlen` `(` `$s` `);` `echo` `getSubSeq(` `$s` `, ` `$n` `);` `// This code is contributed by` `// Akanksha Rai` `?>` |

## Javascript

`<script>` `// Javascript implementation of the approach` `// Function to return the lexicographically` `// largest sub-sequence of s` `function` `getSubSeq(s, n)` `{` ` ` `var` `res = ` `""` `;` ` ` `var` `cr = 0;` ` ` `while` `(cr < n) {` ` ` `// Get the max character from the string` ` ` `var` `mx = s[cr].charCodeAt(0);` ` ` `for` `(` `var` `i = cr + 1; i < n; i++)` ` ` `mx = Math.max(mx, s[i].charCodeAt(0));` ` ` `var` `lst = cr;` ` ` `// Use all the occurrences of the` ` ` `// current maximum character` ` ` `for` `(` `var` `i = cr; i < n; i++)` ` ` `if` `(s[i].charCodeAt(0) == mx) {` ` ` `res += s[i];` ` ` `lst = i;` ` ` `}` ` ` `// Repeat the steps for the remaining string` ` ` `cr = lst + 1;` ` ` `}` ` ` `return` `res;` `}` `// Driver code` `var` `s = ` `"geeksforgeeks"` `;` `var` `n = s.length;` `document.write( getSubSeq(s, n));` `// This code is contributed by famously.` `</script>` |

**Output:**

ss

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

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