# Generating distinct subsequences of a given string in lexicographic order

• Difficulty Level : Hard
• Last Updated : 18 May, 2021

Given a string s, make a list of all possible combinations of letters of a given string S. If there are two strings with the same set of characters, print the lexicographically smallest arrangement of the two strings
For string abc, the list in lexicographic order subsequences are, a ab abc ac b bc c
Examples:

```Input : s = "ab"
Output : a ab b

Input  : xyzx
Output : x xx xy xyx xyz xyzx xz xzx y
yx yz yzx z zx```

The idea is to use a set (which is implemented using self balancing BST) to store subsequences so that duplicates can be tested.
To generate all subsequences, we one by one remove every character and recur for remaining string.

## C++

 `// C++ program to print all distinct subsequences` `// of a string.` `#include ` `using` `namespace` `std;`   `// Finds and stores result in st for a given` `// string s.` `void` `generate(set& st, string s)` `{` `    ``if` `(s.size() == 0)` `        ``return``;`   `    ``// If current string is not already present.` `    ``if` `(st.find(s) == st.end()) {` `        ``st.insert(s);`   `        ``// Traverse current string, one by one` `        ``// remove every character and recur.` `        ``for` `(``int` `i = 0; i < s.size(); i++) {` `            ``string t = s;` `            ``t.erase(i, 1);` `            ``generate(st, t);` `        ``}` `    ``}` `    ``return``;` `}`   `// Driver code` `int` `main()` `{` `    ``string s = ``"xyz"``;` `    ``set st;` `    ``set::iterator it;` `    ``generate(st, s);` `    ``for` `(``auto` `it = st.begin(); it != st.end(); it++)` `        ``cout << *it << endl;` `    ``return` `0;` `}`

## Java

 `// Java program to print all distinct subsequences` `// of a string.` `import` `java.util.*;`   `class` `GFG {`   `    ``// Finds and stores result in st for a given` `    ``// string s.` `    ``static` `void` `generate(Set st, String s)` `    ``{` `        ``if` `(s.length() == ``0``) {` `            ``return``;` `        ``}`   `        ``// If current string is not already present.` `        ``if` `(!st.contains(s)) {` `            ``st.add(s);`   `            ``// Traverse current string, one by one` `            ``// remove every character and recur.` `            ``for` `(``int` `i = ``0``; i < s.length(); i++) {` `                ``String t = s;` `                ``t = t.substring(``0``, i) + t.substring(i + ``1``);` `                ``generate(st, t);` `            ``}` `        ``}` `        ``return``;` `    ``}`   `    ``// Driver code` `    ``public` `static` `void` `main(String args[])` `    ``{` `        ``String s = ``"xyz"``;` `        ``TreeSet st = ``new` `TreeSet<>();` `        ``generate(st, s);` `        ``for` `(String str : st) {` `            ``System.out.println(str);` `        ``}` `    ``}` `}`   `// This code has been contributed by 29AjayKumar` `// modified by rahul_107`

## Python 3

 `# Python program to print all distinct ` `# subsequences of a string.`   `# Finds and stores result in st for a given` `# string s.` `def` `generate(st, s):` `    ``if` `len``(s) ``=``=` `0``:` `        ``return`   `    ``# If current string is not already present.` `    ``if` `s ``not` `in` `st:` `        ``st.add(s)`   `        ``# Traverse current string, one by one` `        ``# remove every character and recur.` `        ``for` `i ``in` `range``(``len``(s)):` `            ``t ``=` `list``(s).copy()` `            ``t.remove(s[i])` `            ``t ``=` `''.join(t)` `            ``generate(st, t)`   `    ``return`     `# Driver Code` `if` `__name__ ``=``=` `"__main__"``:` `    ``s ``=` `"xyz"` `    ``st ``=` `set``()` `    ``generate(st, s)` `    ``for` `i ``in` `st:` `        ``print``(i)`   `# This code is contributed by` `# sanjeev2552`

## C#

 `// C# program to print all distinct subsequences` `// of a string.` `using` `System;` `using` `System.Collections.Generic;`   `class` `GFG {`   `    ``// Finds and stores result in st for a given` `    ``// string s.` `    ``static` `void` `generate(HashSet st, String s)` `    ``{` `        ``if` `(s.Length == 0) {` `            ``return``;` `        ``}`   `        ``// If current string is not already present.` `        ``if` `(!st.Contains(s)) {` `            ``st.Add(s);`   `            ``// Traverse current string, one by one` `            ``// remove every character and recur.` `            ``for` `(``int` `i = 0; i < s.Length; i++) {` `                ``String t = s;` `                ``t = t.Substring(0, i) + t.Substring(i + 1);` `                ``generate(st, t);` `            ``}` `        ``}` `        ``return``;` `    ``}`   `    ``// Driver code` `    ``public` `static` `void` `Main(String[] args)` `    ``{` `        ``String s = ``"xyz"``;` `        ``HashSet st = ``new` `HashSet();` `        ``generate(st, s);` `        ``foreach``(String str ``in` `st)` `        ``{` `            ``Console.WriteLine(str);` `        ``}` `    ``}` `}`   `/* This code contributed by PrinciRaj1992 */`

## Javascript

 ``

Output:

```x
xy
xyz
xz
y
yz
z```

This article is contributed by SANDEEP GAUR MNNIT. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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