[LintCode] Longest Common Prefix

  public String longestCommonPrefix(String[] strs) {
        // write your code here
        if(strs == null || strs.length == 0)
            return "";
        String prefix = strs[0];
        for(int i = 1; i < strs.length; i++) {
            int j = 0;
            while(j < prefix.length() && j < strs[i].length() && prefix.charAt(j)==strs[i].charAt(j))
                j++;
            prefix = prefix.substring(0,j);
        }
        return prefix;
    }