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Java Program To Find Longest Common Prefix Using Sorting

  • Last Updated : 10 Jan, 2022

Problem Statement: Given a set of strings, find the longest common prefix.
Examples: 
 

Input: {"geeksforgeeks", "geeks", "geek", "geezer"}
Output: "gee"

Input: {"apple", "ape", "april"}
Output: "ap"

 

The longest common prefix for an array of strings is the common prefix between 2 most dissimilar strings. For example, in the given array {“apple”, “ape”, “zebra”}, there is no common prefix because the 2 most dissimilar strings of the array “ape” and “zebra” do not share any starting characters. 
We have discussed five different approaches in below posts. 
 

  1. Word by Word Matching
  2. Character by Character Matching
  3. Divide and Conquer
  4. Binary Search.
  5. Using Trie)

 

In this post a new method based on sorting is discussed. The idea is to sort the array of strings and find the common prefix of the first and last string of the sorted array.
 

Java




// Java program to find longest common prefix of
// given array of words.
import java.util.*;
  
public class GFG
{
    public String longestCommonPrefix(String[] a)
    {
        int size = a.length;
  
        /* if size is 0, return empty string */
        if (size == 0)
            return "";
  
        if (size == 1)
            return a[0];
  
        /* sort the array of strings */
        Arrays.sort(a);
  
        /* find the minimum length from first and last string */
        int end = Math.min(a[0].length(), a[size-1].length());
  
        /* find the common prefix between the first and
           last string */
        int i = 0;
        while (i < end && a[0].charAt(i) == a[size-1].charAt(i) )
            i++;
  
        String pre = a[0].substring(0, i);
        return pre;
    }
  
    /* Driver Function to test other function */
    public static void main(String[] args)
    {
        GFG gfg = new GFG();
        String[] input = {"geeksforgeeks", "geeks", "geek", "geezer"};
        System.out.println( "The longest Common Prefix is : " +
                                   gfg.longestCommonPrefix(input));
    }
}

Output: 
 

The longest common prefix is : gee

Time Complexity: O(MAX * n * log n ) where n is the number of strings in the array and MAX is maximum number of characters in any string. Please note that comparison of two strings would take at most O(MAX) time and for sorting n strings, we would need O(MAX * n * log n ) time.
Please refer complete article on Longest Common Prefix using Sorting for more details!


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