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

longestCommonPrefix.java

public class Solution {
    public String longestCommonPrefix(String[] strs) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int size = strs.length;
        if(size == 0) {
            return "";
        }
        
        String common = strs[0];
        
        for (int i = 1; i < size; i++){
            String ahead = strs[i];
            common = longestCommonPrefixHelper(common, ahead);
        }
        
        return common;
    }
    
    public String longestCommonPrefixHelper(String common, String next) {
        int size = (common.length() >= next.length()) ? next.length() : common.length();
        StringBuffer sb = new StringBuffer();
        
        for(int i = 0; i < size; i++) {
            if(common.charAt(i) == next.charAt(i)) {
                sb.append(common.charAt(i));
            } else {
                i = size;
            }
        }
        
        return sb.toString();
    }
}