new_contents: class Solution:
      # @param haystack, a string
      # @param needle, a string
      # @return an integer
  
      def strStr(self, haystack, needle):
          n, m = len(haystack), len(needle)
          if n < m:
              return -1
          i = j = k = 0
          while i+m <= n:
              while j < m and haystack[k] == needle[j]:
                  k += 1
                  j += 1
              if j == m:
                  return i
              i += 1
              k = i
              j = 0
          return -1
  
subject: add solution for Implement strStr