Find a Longest Common Prefix for multiple string using Java

A string prefix is a character(s) at the beginning of a string.

For Example: in apple, app or ap or apps etc are prefix

Problem

Find the common longest prefix for strings apple, apps and appster

Approach

1. Sort all the string in alphabetical order.
2. Find the small string
3. Loop through the small string by each character.
4. Compare each character in other string at same index.
5. If in any iteration there is no match of any character at any index, Exit.
6. String of all character before #5 is your common prefix

Code

import java.util.ArrayList;
import java.util.List;

public class PrefixFinder {
	
	public static void main(String[] args) {
		List<String> fruits = new ArrayList<String>();		
		fruits.add("apple");		
		fruits.add("apps");
		fruits.add("appster");
		
		String str = fruits.get(0);
		
		//find the short value
		for(String fruit: fruits) {
			if (str.length() > fruit.length()) {
				str = fruit;
			}
		}
		
		System.out.println("small string is " + str);
		String pref = "";
		Boolean flag = false;
		for(int i = 0; i < str.length(); i++) {			
			char c = str.charAt(i);
			for(int j=0; j<fruits.size(); j++) {
				if(fruits.get(j).charAt(i) != c) {
					flag = true;
					break;
				} 
			}
			
			if(flag == false) {
				pref = pref + c;
			}			
			
		}
		
		System.out.println("prefix is " + pref);        
	}

}

Run Code