0454-4sum-ii.py

#两两求和
class Solution:
    def fourSumCount(self, nums1: List[int], nums2: List[int], nums3: List[int], nums4: List[int]) -> int:
        mapper = {}
        res = 0
        for i in nums1:
            for j in nums2:
                mapper[i + j] = mapper.get(i + j, 0) + 1
        for i in nums3:
            for j in nums4:
                res += mapper.get(-1 * (i + j), 0)
        return res