new_contents: class Solution:
      # @return a string
  
      def longestCommonPrefix(self, strs):
          if not strs:
              return ''
          return reduce(self.lcs, strs)
  
      def lcs(self, sa, sb):
          res = 0
          for i in xrange(min(len(sa), len(sb))):
              if sa[i] != sb[i]:
                  break
              res += 1
          return sa[:res]
  
subject: add solution for Longest Common Prefix