最長公共前綴

本來用的find，發現速度太慢，看了看大神的，是每位做比較，因此改了：

class Solution:
    def longestCommonPrefix(self, strs: List[str]) -> str:
        if len(strs) == 0:
            return ""
        maxstr = max(strs)
        minstr = min(strs)
        lens = len(minstr)
        result = ""
        for i in range(lens):
            prefind = minstr[i]
            for j in strs:
                #key = j.find(prefind)
                if prefind != j[i]:
                    return result
            result = minstr[:i+1]
        return result