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# Find shortest unique prefix for every word in a given list | Set 2 (Using Sorting)

• Difficulty Level : Hard
• Last Updated : 12 Jun, 2021

Given an array of words, find all shortest unique prefixes to represent each word in the given array. Assume that no word is a prefix of another. Output the shortest unique prefixes in sorted order.

```Input  : {"zebra", "dog", "duck", "dove"}
Output : z, dog, dov, du
Explanation: dog => dog
dove = dov
duck = du
z   => zebra

Input: {"geeksgeeks", "geeksquiz", "geeksforgeeks"}
Output: geeksf, geeksg, geeksq```

We have discussed a Trie based approach in the below post.
Find shortest unique prefix for every word in a given list | Set 1 (Using Trie)
In this post, a sorting based approach is discussed. On comparing the string with 2 other most similar strings in the array, we can find its shortest unique prefix. For example, if we sort the array {“zebra”, “dog”, “duck”, “dove”}, we get {“dog”, “dove”, “duck”, “zebra”}. The shortest unique prefix for the string “dove” can be found as:
Compare “dove” to “dog” –> unique prefix for dove is “dov”
Compare “dove” to “duck” –> unique prefix for dove is “do”
Now, the shortest unique prefix for “dove” is the one with greater length between “dov” and “do”. So, it is “dov”.
The shortest unique prefix for the first and last string can be found by comparing them with only 1 most similar neighbor on right and left, respectively.

We can sort the array of strings and keep on doing this for every string of the array.

## C++

 `// C++ program to print shortest unique prefixes``// for every word.``#include ``using` `namespace` `std;` `vector uniquePrefix(vector &a)``{``    ``int` `size = a.size();` `    ``/* create an array to store the results */``    ``vector res(size);` `    ``/* sort the array of strings */``    ``sort(a.begin(), a.end());` `    ``/* compare the first string with its only right``    ``neighbor */``    ``int` `j = 0;``    ``while` `(j < min(a.length() - 1, a.length() - 1))``    ``{``        ``if` `(a[j] == a[j])``            ``j++;``        ``else``            ``break``;``    ``}``    ``int` `ind = 0;``    ``res[ind++] = a.substr(0, j + 1);` `    ``/* Store the unique prefix of a from its left neighbor */``    ``string temp_prefix = a.substr(0, j + 1);``    ``for` `(``int` `i = 1; i < size - 1; i++)``    ``{``        ``/* compute common prefix of a[i] unique from``        ``its right neighbor */``        ``j = 0;``        ``while` `(j < min(a[i].length() - 1, a[i + 1].length() - 1))``        ``{``            ``if` `(a[i][j] == a[i + 1][j])``                ``j++;``            ``else``                ``break``;``        ``}` `        ``string new_prefix = a[i].substr(0, j + 1);` `        ``/* compare the new prefix with previous prefix */``        ``if` `(temp_prefix.length() > new_prefix.length())``            ``res[ind++] = temp_prefix;``        ``else``            ``res[ind++] = new_prefix;` `        ``/* store the prefix of a[i+1] unique from its``        ``left neighbour */``        ``temp_prefix = a[i + 1].substr(0, j + 1);``    ``}` `    ``/* compute the unique prefix for the last string``    ``in sorted array */``    ``j = 0;``    ``string sec_last = a[size - 2];` `    ``string last = a[size - 1];` `    ``while` `(j < min(sec_last.length() - 1, last.length() - 1))``    ``{``        ``if` `(sec_last[j] == last[j])``            ``j++;``        ``else``            ``break``;``    ``}` `    ``res[ind] = last.substr(0, j + 1);``    ``return` `res;``}` `// Driver Code``int` `main()``{``    ``vector input = {``"zebra"``, ``"dog"``, ``"duck"``, ``"dove"``};``    ``vector output = uniquePrefix(input);``    ``cout << ``"The shortest unique prefixes in sorted order are : \n"``;` `    ``for` `(``auto` `i : output)``        ``cout << i << ``' '``;` `    ``return` `0;``}` `// This code is contributed by``// sanjeev2552`

## Java

 `// Java program to print shortest unique prefixes``// for every word.``import` `java.io.*;``import` `java.util.*;` `class` `GFG``{``    ``public` `String[] uniquePrefix(String[] a)``    ``{``        ``int` `size = a.length;` `        ``/* create an array to store the results */``        ``String[] res = ``new` `String[size];` `        ``/* sort the array of strings */``        ``Arrays.sort(a);` `        ``/* compare the first string with its only right``           ``neighbor */``        ``int` `j = ``0``;``        ``while` `(j < Math.min(a[``0``].length()-``1``, a[``1``].length()-``1``))``        ``{``            ``if` `(a[``0``].charAt(j)==a[``1``].charAt(j))``                ``j++;``            ``else``                ``break``;``        ``}`  `        ``int` `ind = ``0``;``        ``res[ind++] = a[``0``].substring(``0``, j+``1``);` `        ``/* Store the unique prefix of a from its left neighbor */``        ``String temp_prefix = a[``1``].substring(``0``, j+``1``);``        ``for` `(``int` `i = ``1``; i < size-``1``; i++)``        ``{``            ``/* compute common prefix of a[i] unique from``               ``its right neighbor */``            ``j = ``0``;``            ``while` `(j < Math.min( a[i].length()-``1``, a[i+``1``].length()-``1` `))``            ``{``                ``if` `(a[i].charAt(j) == a[i+``1``].charAt(j))``                    ``j++;``                ``else``                    ``break``;``            ``}` `            ``String new_prefix = a[i].substring(``0``, j+``1``);` `            ``/* compare the new prefix with previous prefix */``            ``if` `(temp_prefix.length() > new_prefix.length() )``                ``res[ind++] = temp_prefix;``            ``else``                ``res[ind++] = new_prefix;` `            ``/* store the prefix of a[i+1] unique from its``               ``left neighbour */``            ``temp_prefix = a[i+``1``].substring(``0``, j+``1``);``        ``}` `        ``/* compute the unique prefix for the last string``           ``in sorted array */``        ``j = ``0``;``        ``String sec_last = a[size-``2``] ;` `        ``String last = a[size-``1``];` `        ``while` `(j < Math.min( sec_last.length()-``1``, last.length()-``1``))``        ``{``            ``if` `(sec_last.charAt(j) == last.charAt(j))``                ``j++;``            ``else``                ``break``;``        ``}` `        ``res[ind] = last.substring(``0``, j+``1``);``        ``return` `res;``    ``}` `    ``/* Driver Function to test other function */``    ``public` `static` `void` `main(String[] args)``    ``{``        ``GFG gfg = ``new` `GFG();` `        ``String[] input = {``"zebra"``, ``"dog"``, ``"duck"``, ``"dove"``};` `        ``String[] output = gfg.uniquePrefix(input);``        ``System.out.println( ``"The shortest unique prefixes"` `+``                               ``" in sorted order are :"``);` `        ``for` `(``int` `i=``0``; i < output.length; i++)``            ``System.out.print( output[i] + ``" "``);``    ``}``}`

## Python3

 `# Python3 program to prshortest unique prefixes``# for every word.``def` `uniquePrefix(a):``    ` `    ``size ``=` `len``(a)` `    ``# Create an array to store the results``    ``res ``=` `[``0``] ``*` `(size)` `    ``# Sort the array of strings */``    ``a ``=` `sorted``(a)` `    ``# Compare the first with its only right``    ``# neighbor``    ``j ``=` `0``    ``while` `(j < ``min``(``len``(a[``0``]) ``-` `1``, ``len``(a[``1``]) ``-` `1``)):``        ``if` `(a[``0``][j] ``=``=` `a[``1``][j]):``            ``j ``+``=` `1``        ``else``:``            ``break` `    ``ind ``=` `0``    ``res[ind] ``=` `a[``0``][``0``:j ``+` `1``]``    ``ind ``+``=` `1` `    ``# Store the unique prefix of a``    ``# from its left neighbor``    ``temp_prefix ``=` `a[``1``][``0``:j ``+` `1``]``    ``for` `i ``in` `range``(``1``, size ``-` `1``):``        ` `        ``# Compute common prefix of a[i] unique from``        ``# its right neighbor``        ``j ``=` `0``        ` `        ``while` `(j < ``min``(``len``(a[i]) ``-` `1``, ``len``(a[i ``+` `1``]) ``-` `1``)):``            ``if` `(a[i][j] ``=``=` `a[i ``+` `1``][j]):``                ``j ``+``=` `1``            ``else``:``                ``break` `        ``new_prefix ``=` `a[i][``0``:j ``+` `1``]` `        ``# Compare the new prefix with previous prefix``        ``if` `(``len``(temp_prefix) > ``len``(new_prefix)):``            ``res[ind] ``=` `temp_prefix``            ``ind ``+``=` `1``        ``else``:``            ``res[ind] ``=` `new_prefix``            ``ind ``+``=` `1` `        ``# Store the prefix of a[i+1] unique from its``        ``# left neighbour``        ``temp_prefix ``=` `a[i ``+` `1``][``0``:j ``+` `1``]` `    ``# Compute the unique prefix for the last``    ``# in sorted array``    ``j ``=` `0``    ``sec_last ``=` `a[size ``-` `2``]` `    ``last ``=` `a[size ``-` `1``]` `    ``while` `(j < ``min``(``len``(sec_last) ``-` `1``, ``len``(last) ``-` `1``)):``        ``if` `(sec_last[j] ``=``=` `last[j]):``            ``j ``+``=` `1``        ``else``:``            ``break` `    ``res[ind] ``=` `last[``0``:j ``+` `1``]``    ``return` `res` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ` `    ``input` `=` `[ ``"zebra"``, ``"dog"``, ``"duck"``, ``"dove"` `]``    ``output ``=` `uniquePrefix(``input``)``    ` `    ``print``(``"The shortest unique prefixes "` `+``          ``"in sorted order are : "``)` `    ``for` `i ``in` `output:``        ``print``(i, end ``=` `" "``)``        ` `# This code is contributed by mohit kumar 29`

## C#

 `// C# program to print shortest unique prefixes``// for every word.``using` `System;``    ` `class` `GFG``{``    ``public` `String[] uniquePrefix(String[] a)``    ``{``        ``int` `size = a.Length;` `        ``/* create an array to store the results */``        ``String[] res = ``new` `String[size];` `        ``/* sort the array of strings */``        ``Array.Sort(a);` `        ``/* compare the first string with its only right``        ``neighbor */``        ``int` `j = 0;``        ``while` `(j < Math.Min(a.Length - 1, a.Length - 1))``        ``{``            ``if` `(a[j] == a[j])``                ``j++;``            ``else``                ``break``;``        ``}`  `        ``int` `ind = 0;``        ``res[ind++] = a.Substring(0, j + 1);` `        ``/* Store the unique prefix of a from its left neighbor */``        ``String temp_prefix = a.Substring(0, j + 1);``        ``for` `(``int` `i = 1; i < size - 1; i++)``        ``{``            ``/* compute common prefix of a[i] unique from``            ``its right neighbor */``            ``j = 0;``            ``while` `(j < Math.Min( a[i].Length - 1, a[i + 1].Length - 1 ))``            ``{``                ``if` `(a[i][j] == a[i + 1][j])``                    ``j++;``                ``else``                    ``break``;``            ``}` `            ``String new_prefix = a[i].Substring(0, j+1);` `            ``/* compare the new prefix with previous prefix */``            ``if` `(temp_prefix.Length > new_prefix.Length )``                ``res[ind++] = temp_prefix;``            ``else``                ``res[ind++] = new_prefix;` `            ``/* store the prefix of a[i+1] unique from its``            ``left neighbour */``            ``temp_prefix = a[i+1].Substring(0, j+1);``        ``}` `        ``/* compute the unique prefix for the last string``        ``in sorted array */``        ``j = 0;``        ``String sec_last = a[size-2] ;` `        ``String last = a[size-1];` `        ``while` `(j < Math.Min( sec_last.Length-1, last.Length-1))``        ``{``            ``if` `(sec_last[j] == last[j])``                ``j++;``            ``else``                ``break``;``        ``}` `        ``res[ind] = last.Substring(0, j+1);``        ``return` `res;``    ``}` `    ``/* Driver code */``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``GFG gfg = ``new` `GFG();` `        ``String[] input = {``"zebra"``, ``"dog"``, ``"duck"``, ``"dove"``};` `        ``String[] output = gfg.uniquePrefix(input);``        ``Console.WriteLine( ``"The shortest unique prefixes"` `+``                            ``" in sorted order are :"``);` `        ``for` `(``int` `i = 0; i < output.Length; i++)``            ``Console.Write( output[i] + ``" "``);``    ``}``}` `// This code is contributed by Princi Singh`

Output:

```The shortest unique prefixes in sorted order are :
dog dov du z ```

Another Python approach:
If we want to output the prefixes as the order of strings in the input array, we can store the string and its corresponding index in the hashmap. While adding the prefix to the result array, we can get the index of the corresponding string from the hashmap and add the prefix to that index.

## Python3

 `#Python program to print shortest unique prefix for every word in a list` `a``=``[``'dogs'``,``'dove'``,``'duck'``,``'zebra'``]``r``=``[]``j``=``0``while``(j<``min``(``len``(a[``0``]),``len``(a[``1``]))):``    ``if``(a[``0``][j]``=``=``a[``1``][j]):``        ``j``+``=``1``    ``else``:``        ``break` `i``=``0``r.append(a[``0``][``0``:j``+``1``])``x``=``a[``1``][``0``:j``+``1``]` `for` `i ``in` `range``(``1``,``len``(a)``-``1``):``    ``j``=``0``    ``while``(j<``min``(``len``(a[i]),``len``(a[i``+``1``]))):``        ``if` `a[i][j]``=``=``a[i``+``1``][j]:``            ``j``+``=``1``        ``else``:``            ``break` `    ``y``=``a[i][``0``:j``+``1``]``    ``if``(``len``(x)>``len``(y)):``        ``r.append(x)``    ``else``:``        ``r.append(y)``    ``x``=``a[i``+``1``][``0``:j``+``1``]``    ` `j``=``0``l``=``a[``len``(a)``-``2``]``k``=``a[``len``(a)``-``1``]` `while``(j<``min``(``len``(l),``len``(k))):``    ``if` `( l[j]``=``=``k[j]):``        ``j``+``=``1``    ``else``:``        ``break``        ` `r.append(k[``0``:j``+``1``])``print``(``"The shortest unique prefixes are :"``)``for` `i ``in` `range``(``0``,``len``(r)):``  ``print``(r[i],end``=``' '``)``  ` ` ``#This code is contributed by Saahith Reddy`

Output:

```The shortest unique prefixes are :
dog dov du z```

For a more efficient solution, we can use Trie as discussed in this post.
This article is contributed by Saloni Baweja. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.