14. 最长公共前缀

输入: ["flower","flow","flight"]
输出: "fl"

输入: ["dog","racecar","car"]
输出: ""
解释: 输入不存在公共前缀。

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) {
            return "";
        }
        String pre = strs[0];
        int i = 1;
        while (i < strs.length) {
            while (strs[i].indexOf(pre) != 0) {
                pre = pre.substring(0, pre.length() - 1);
            }
            i++;
        }
        return pre;
    }
}