[LeetCode] 14. Longest Common Prefix

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

 public class Solution {
     public String longestCommonPrefix(String[] strs) {
         if (strs == null || strs.length == 0) {
             return "";
         } else if (strs.length < 2) {
             return strs[0];
         }

         String r = strs[0];
         int index = r.length();
         for (int i = 1; i < strs.length; i++) {
             int j = 0;
             for (; j < strs[i].length() && j < index; j++) {
                 if (strs[i].charAt(j) != r.charAt(j)) {
                     break;
                 }
             }
             if (j == 0) {
                 return "";
             }
             index = j;
         }

         return r.substring(0, index);
     }
 }