找出最长的公共前缀子串

示例1：

输入：["abcde","abcfk","abcgggd"]

输出："abc"

示例2：
输入：["how","what","when"]

输出：""

Python解决方案：

class Solution(object):
    def longestCommonPrefix(self, strs):
        """
        :type strs: List[str]
        :rtype: str
        """
        if not strs:
            return ""
        elif len(strs) == 1:
            return strs[0]
        else:
            out = ""
            f_len = len(strs[0])
            m = 0
            while m < f_len:
                first = strs[0][m]
                for i in strs[1:]:
                    if m > len(i)-1 or i[m] != first:
                        return out
                out += i[m]
                m += 1
            return out