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# Smallest string containing all unique characters from given array of strings

Given an array of strings arr[], the task is to find the smallest string which contains all the characters of the given array of strings.

Examples:

Input: arr[] = {“your”, “you”, “or”, “yo”}
Output: ruyo
Explanation: The string “ruyo” is the smallest string which contains all the characters that are used across all the strings of the given array.

Input: arr[] = {“abm”, “bmt”, “cd”, “tca”}
Output: abctdm

Approach: This problem can be solved by using the Set Data Structure. Set has the capability to remove duplicates, which is needed in this problem in order to minimize the string size. Add all the characters in the set from all the strings in the array arr[] and form a string containing all the characters remaining in the set, which is the required answer.

Below is the implementation of the above approach.

## C++

 `// C++ code for the above approach` `#include ` `using` `namespace` `std;`   `string minSubstr(vector s)` `{` `  `  `    ``// Stores the concatenated string` `    ``// of all the given strings` `    ``string str = ``""``;`   `    ``// Loop to iterate through all` `    ``// the given strings` `    ``for` `(``int` `i = 0; i < s.size(); i++)` `    ``{` `        ``str += s[i];` `    ``}`   `    ``// Set to store the characters` `    ``unordered_set<``char``> set;`   `    ``// Loop to iterate over all` `    ``// the characters in str` `    ``for` `(``int` `i = 0; i < str.length(); i++)` `    ``{` `        ``set.insert(str[i]);` `    ``}` `    ``string res = ``""``;` `  `  `    ``// Loop to iterate over the set` `    ``for` `(``auto` `itr = set.begin(); itr != set.end(); itr++)` `    ``{` `        ``res = res + (*itr);` `    ``}`   `    ``// Return Answer` `    ``return` `res;` `}`   `// Driver Code` `int` `main()` `{` `    ``vector arr = {``"your"``, ``"you"``,` `                          ``"or"``, ``"yo"``};`   `    ``cout << (minSubstr(arr));` `    ``return` `0;` `}`   `// This code is contributed by Potta Lokesh`

## Java

 `import` `java.util.*;`   `public` `class` `GfG {`   `    ``public` `static` `String minSubstr(String s[])` `    ``{` `        ``// Stores the concatenated string` `        ``// of all the given strings` `        ``String str = ``""``;`   `        ``// Loop to iterate through all` `        ``// the given strings` `        ``for` `(``int` `i = ``0``; i < s.length; i++) {` `            ``str += s[i];` `        ``}`   `        ``// Set to store the characters` `        ``Set set` `            ``= ``new` `HashSet();`   `        ``// Loop to iterate over all` `        ``// the characters in str` `        ``for` `(``int` `i = ``0``; i < str.length(); i++) {` `            ``set.add(str.charAt(i));` `        ``}`   `        ``// Stores the required answer` `        ``String res = ``""``;` `        ``Iterator itr` `            ``= set.iterator();`   `        ``// Loop to iterate over the set` `        ``while` `(itr.hasNext()) {` `            ``res += itr.next();` `        ``}`   `        ``// Return Answer` `        ``return` `res;` `    ``}`   `    ``// Driver Code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``String arr[]` `            ``= ``new` `String[] { ``"your"``, ``"you"``,` `                             ``"or"``, ``"yo"` `};`   `        ``System.out.println(minSubstr(arr));` `    ``}` `}`

## Python3

 `# Python code for the above approach` `def` `minSubstr(s):`   `    ``# Stores the concatenated string` `    ``# of all the given strings` `    ``str` `=` `""`   `    ``# Loop to iterate through all` `    ``# the given strings` `    ``for` `i ``in` `range``(``len``(s)):` `        ``str` `+``=` `s[i]`   `    ``# Set to store the characters` `    ``_set ``=` `set``()`   `    ``# Loop to iterate over all` `    ``# the characters in str` `    ``for` `i ``in` `range``(``len``(``str``)):` `        ``_set.add(``str``[i])`   `    ``# Stores the required answer` `    ``res ``=` `""`   `    ``# Loop to iterate over the set` `    ``for` `itr ``in` `_set:` `        ``res ``+``=` `itr`   `    ``# Return Answer` `    ``return` `res`   `# Driver Code` `arr ``=` `[``"your"``, ``"you"``, ``"or"``, ``"yo"``]` `print``(minSubstr(arr))`   `# This code is contributed by gfgking`

## C#

 `// C# program for the above approach` `using` `System;` `using` `System.Collections.Generic;`   `class` `GFG` `{` `    ``public` `static` `string` `minSubstr(``string` `[]s)` `    ``{` `        ``// Stores the concatenated string` `        ``// of all the given strings` `        ``string` `str = ``""``;`   `        ``// Loop to iterate through all` `        ``// the given strings` `        ``for` `(``int` `i = 0; i < s.Length; i++) {` `            ``str += s[i];` `        ``}`   `        ``// Set to store the characters` `        ``HashSet<``char``> ``set` `= ``new` `HashSet<``char``>();`   `        ``// Loop to iterate over all` `        ``// the characters in str` `        ``for` `(``int` `i = 0; i < str.Length; i++) {` `            `  `            ``set``.Add(str[i]);` `        ``}`   `        ``// Stores the required answer` `        ``String res = ``""``;`   `        ``// Loop to iterate over the set` `        ``foreach``(``char` `i ``in` `set``) {` `            ``res += i;` `        ``}`   `        ``// Return Answer` `        ``return` `res;` `    ``}`   `    ``// Driver Code` `    ``public` `static` `void` `Main()` `    ``{` `        ``string` `[]arr` `            ``= { ``"your"``, ``"you"``, ``"or"``, ``"yo"` `};`   `        ``Console.WriteLine(minSubstr(arr));` `    ``}` `}` `// This code is contributed by Samim Hossain Mondal.`

## Javascript

 `  ```

Output

`ruoy`

Time Complexity: O(N*M), where M is the average length of strings in the given array
Auxiliary Space: O(N) because extra space for string str is being used

Approach #2: This problem can also be solved by using the Map Data Structure. Map stores all the characters present in the string with their occurrence. After iterating on the map we will get the all unique characters.

## C++

 `// C++ code for the above approach` `#include ` `using` `namespace` `std;`   `string minSubstr(vector s)` `{`   `    ``// Stores the concatenated string` `    ``// of all the given strings` `    ``string str = ``""``;`   `    ``// Loop to iterate through all` `    ``// the given strings` `    ``for` `(``int` `i = 0; i < s.size(); i++) {` `        ``str += s[i];` `    ``}`   `    ``// map to store the characters with frequency` `    ``unordered_map<``char``, ``int``> mp;`   `    ``// Loop to iterate over all` `    ``// the characters in str` `    ``for` `(``int` `i = 0; i < str.length(); i++) {` `        ``mp[str[i]]++;` `    ``}` `    ``string res = ``""``;`   `    ``// Loop to iterate over the map` `    ``for` `(``auto` `it : mp) {` `        ``res += it.first;` `    ``}`   `    ``// Return Answer` `    ``return` `res;` `}`   `// Driver Code` `int` `main()` `{` `    ``vector arr = { ``"your"``, ``"you"``, ``"or"``, ``"yo"` `};`   `    ``cout << (minSubstr(arr));` `    ``return` `0;` `}`   `// This code is contributed by Prasad Kandekar(prasad264)`

## Java

 `// Java code for the above approach` `import` `java.util.*;` `class` `GFG {` `  ``public` `static` `String minSubstr(List s)` `  ``{`   `    ``// Stores the concatenated string` `    ``// of all the given strings` `    ``String str = ``""``;`   `    ``// Loop to iterate through all` `    ``// the given strings` `    ``for` `(String x : s) {` `      ``str += x;` `    ``}`   `    ``// map to store the characters with frequency` `    ``Map mp = ``new` `HashMap<>();`   `    ``// Loop to iterate over all` `    ``// the characters in str` `    ``for` `(``int` `i = ``0``; i < str.length(); i++) {` `      ``char` `c = str.charAt(i);` `      ``if` `(mp.containsKey(c)) {` `        ``mp.put(c, mp.get(c) + ``1``);` `      ``}` `      ``else` `{` `        ``mp.put(c, ``1``);` `      ``}` `    ``}`   `    ``StringBuilder res = ``new` `StringBuilder();`   `    ``// Loop to iterate over the map` `    ``for` `(Map.Entry entry :` `         ``mp.entrySet()) {` `      ``res.append(entry.getKey());` `    ``}`   `    ``// Return Answer` `    ``return` `res.toString();` `  ``}`   `  ``// Driver Code` `  ``public` `static` `void` `main(String[] args)` `  ``{` `    ``List arr` `      ``= Arrays.asList(``"your"``, ``"you"``, ``"or"``, ``"yo"``);` `    ``System.out.println(minSubstr(arr));` `  ``}` `}`   `// This code is contributed by Prasad Kandekar(prasad264)`

## Python3

 `# Python code for the above approach`   `def` `min_substr(s):` `    ``# Stores the concatenated string` `    ``# of all the given strings` `    ``str` `=` `""`   `    ``# Loop to iterate through all` `    ``# the given strings` `    ``for` `i ``in` `range``(``len``(s)):` `        ``str` `+``=` `s[i]`   `    ``# dictionary to store the characters with frequency` `    ``mp ``=` `{}`   `    ``# Loop to iterate over all` `    ``# the characters in str` `    ``for` `i ``in` `range``(``len``(``str``)):` `        ``if` `str``[i] ``in` `mp:` `            ``mp[``str``[i]] ``+``=` `1` `        ``else``:` `            ``mp[``str``[i]] ``=` `1`   `    ``res ``=` `""`   `    ``# Loop to iterate over the map` `    ``for` `key ``in` `mp:` `        ``res ``+``=` `key`   `    ``# Return Answer` `    ``return` `res`   `# Driver Code` `arr ``=` `[``"your"``, ``"you"``, ``"or"``, ``"yo"``]` `print``(min_substr(arr))`   `# This code is contributed by karthik`

## C#

 `// C# code for the above approach` `using` `System;` `using` `System.Collections.Generic;`   `public` `class` `GFG {` `  ``static` `string` `MinSubstr(List<``string``> s)` `  ``{` `    ``// Stores the concatenated string` `    ``// of all the given strings` `    ``string` `str = ``""``;`   `    ``// Loop to iterate through all` `    ``// the given strings` `    ``for` `(``int` `i = 0; i < s.Count; i++) {` `      ``str += s[i];` `    ``}`   `    ``// dictionary to store the characters with frequency` `    ``Dictionary<``char``, ``int``> mp` `      ``= ``new` `Dictionary<``char``, ``int``>();`   `    ``// Loop to iterate over all` `    ``// the characters in str` `    ``for` `(``int` `i = 0; i < str.Length; i++) {` `      ``if` `(mp.ContainsKey(str[i])) {` `        ``mp[str[i]]++;` `      ``}` `      ``else` `{` `        ``mp[str[i]] = 1;` `      ``}` `    ``}`   `    ``string` `res = ``""``;`   `    ``// Loop to iterate over the map` `    ``foreach``(``var` `item ``in` `mp) { res += item.Key; }`   `    ``// Return Answer` `    ``return` `res;` `  ``}`   `  ``// Driver Code` `  ``static` `public` `void` `Main(``string``[] args)` `  ``{` `    ``List<``string``> arr = ``new` `List<``string``>() {` `      ``"your"``, ``"you"``, ``"or"``, ``"yo"` `      ``};`   `    ``Console.WriteLine(MinSubstr(arr));` `  ``}` `}`   `// This code is contributed by Prasad Kandekar(prasad264)`

## Javascript

 `// JavaScript code for the above approach` `function` `minSubstr(s) {`   `    ``// Stores the concatenated string ` `    ``// of all the given strings` `    ``var` `str = ``""``;`   `    ``// Loop to iterate through ` `    ``// all the given strings` `    ``for` `(``var` `i = 0; i < s.length; i++) {` `        ``str += s[i];` `    ``}`   `    ``// map to store the characters with frequency` `    ``var` `mp = ``new` `Map();` `    `  `    ``// Loop to iterate over all ` `    ``// the characters in str` `    ``for` `(``var` `i = 0; i < str.length; i++) {` `        ``if` `(mp.has(str[i])) {` `            ``mp.set(str[i], mp.get(str[i]) + 1);` `        ``}` `        ``else` `{` `            ``mp.set(str[i], 1);` `        ``}` `    ``}`   `    ``var` `res = ``""``;`   `    ``// Loop to iterate over the map` `    ``for` `(``var` `[key, value] of mp) {` `        ``res += key;` `    ``}`   `    ``// Return Answer` `    ``return` `res;` `}`   `// Driver Code` `var` `arr = [``"your"``, ``"you"``, ``"or"``, ``"yo"``];` `console.log(minSubstr(arr));`   `// This code is contributed by Prasad Kandekar(prasad264)`

Output:

`ruoy`

Complexity analysis:

Time Complexity: O(N*M), where M is the average length of strings in the given array
Auxiliary Space: O(N) because extra space for string str and unordered_map are being used

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