Longest Common Prefix

class Solution(object):
    def isSamechar(self,strs,pos):
        if(len(strs[0])<=pos):
            return False
        else:
            for i in range(1,len(strs)):
                if len(strs[i])<=pos or strs[i][pos]!=strs[0][pos]:
                    return False
            return True
    def longestCommon(self,strs,left ,right):
        if left==right:
            if isSamechar(self,strs,left):
                return strs[0][left]
            else:
                return ""
        mid=left+(right-left)/2
        if(len(longestCommon(self,strs,left,mid))==(right-left)/2):
            return longestCommon(self,strs,left,mid)+longestCommon(self.strs,mid,right)
        else:
            return longestCommon(self,strs,left,mid)
        
    def longestCommonPrefix(self, strs):
        """
        :type strs: List[str]
        :rtype: str
        """
        res=longestCommon(self,strs,0,len(strs[0]))
        return res