14. 最长公共前缀

 public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length==0)
            return "";
        String result = "";
        int minLength = strs[0].length();
        for (String st : strs ){
            if (st.length()<minLength) {
                minLength = st.length();
            }
        }
        for (int i = 0; i < minLength; i++) {
           char c = strs[0].charAt(i);
           for (String s :strs) {
               if (s.charAt(i) != c ){
                   return result;
               }
           }
           result += c;
        }
        return  result;
    }