Longest Common Prefix

Write a function to find the longest common prefix string among an array of strings.

Solution:
Basic implementation question. Iterate through all Strings. 

public class Solution {
    public String longestCommonPrefix(String[] strs) {
        if(strs.length == 0) return "";
        char[] c = strs[0].toCharArray(); 
        StringBuilder prefix = new StringBuilder();
        for(int i = 0; i < c.length; i++){
            Boolean flag = true;
            for(int j = 1; j < strs.length; j++){
                if(strs[j].length() - 1 < i || strs[j].charAt(i) != c[i]){ 
                    flag = false;
                    break;
                }
            }
            if(flag == true){
                prefix.append(c[i]);
            }
            else break;
        }
        return prefix.toString();
    }
}