text: class Solution:
      def strStr(self, haystack, needle):
          """
          :type haystack: str
          :type needle: str
          :rtype: int
          """
  
          i = 0
          l1 = len(haystack)
          l2 = len(needle)
  
          if l2 == 0:
              return 0
  
          while i < l1:
              if haystack[i: i + l2] == needle:
                  return i
              i += 1
          return -1