text: class Solution(object):
      def longestCommonPrefix(self, strs):
          """
          :type strs: List[str]
          :rtype: str
          """
          if strs is None :
              return ""
          if not strs:
              return ""
          shortest = min(strs,key=len)
          for i, ch in enumerate(shortest):
              for other in strs:
                  if other[i] != ch:
                      return shortest[:i]
          return shortest