class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) {
            return "";//字符串为空就返回空值
        }
        String prefix = strs[0];//把字符串第一个元素赋值给prefix
        int count = strs.length;//记录字符串长度
        for (int i = 1; i < count; i++) {
            prefix = longestCommonPrefix(prefix, strs[i]);//求公共前缀
            if (prefix.length() == 0) {
                break;//如果prefix长度为0，什么没有公共元素，就跳出循环
            }
        }
        return prefix;
    }

    public String longestCommonPrefix(String str1, String str2) {
        int length = Math.min(str1.length(), str2.length());//取s1和s2的最小长度
        int index = 0;//记录相同元素的截断点
        while (index < length && str1.charAt(index) == str2.charAt(index)) {
            index++;
        }
        return str1.substring(0, index);//将0到index-1的值返回给prefix
    }
}