new_contents: from collections import Counter
  class Solution(object):
      def fourSumCount(self, A, B, C, D):
          """
          :type A: List[int]
          :type B: List[int]
          :type C: List[int]
          :type D: List[int]
          :rtype: int
          """
          count1 = Counter()
          for a in A:
              for b in B:
                  count1[a + b] += 1
          ans = 0
          for c in C:
              for d in D:
                  ans += count1[-(c + d)]
          return ans
  
subject: Add py solution for 454. 4Sum II