Problem Title: Longest Common Prefix in an Array

This Problem is listed in GFG sheet

Problem Statement

Given an array of N strings, find the longest common prefix among all strings present in the array.

Example 1

Input:
N = 4
arr[] = {geeksforgeeks, geeks, geek,
         geezer}
Output: gee
Explanation: "gee" is the longest common
prefix in all the given strings.        

Example 2

Input: 
N = 2
arr[] = {hello, world}
Output: -1
Explanation: There's no common prefix
in the given strings.        

Your Task

You don't need to read input or print anything. Your task is to complete the function longestCommonPrefix() which takes the string array arr[] and its size N as inputs and returns the longest common prefix common in all the strings in the array. If there's no prefix common in all the strings, return -1.

• Expected Time Complexity: O(N*min(|arri|)).
• Expected Auxiliary Space: O(min(|arri|))

Java Code

class Solution{
    String longestCommonPrefix(String arr[], int n){
       if (n == 0) {
            return "-1";
        }
        String res = arr[0];
        for (int i = 1; i < n; i++) {
            while (arr[i].indexOf(res) != 0) {
                res = res.substring(0, res.length() - 1);
                if (res.isEmpty()) {
                    return "-1";
                }
            }
        }
        return res;
    }
}        

Approach

• This problem will find the longest common prefix among an array of strings.
• Initially we need to pass the parameters in the method
• arr : An array of string for which the method longestCommonPrefix will find the longest common prefix. n The number of strings in the array.
• If Condition :
• if there are no string in the array (n == 0) the method returns -1 because there is no common prefix to find.
• If string is present :
• The variable res is initialized with the first string in the array. This will be used to find the common prefix.
• For Loop:
• for(int i = 1; i < n; i++) The loop starts from the second index and iterates each string in the array.
• Checking for common prefix:
• This can be done using while loop
• while(arr[i].indexOf(res) !=0) For each string arr[i] this loop checks if res is a prefix or not.
• The method indexOf(res) will return the index within the string if res is found.
• What if there is no common prefix :

if(res.isEmpty()){
return "-1";
}        

• The above condition will return -1 if there is no common prefix.
• If the res is found return the result.