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);

     }

 }