这类题目基本是用字典 以空间换时间
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
"""
dict1={}
res=0
for i in range(len(A)):
for j in range(len(B)):
if not A[i]+B[j] in dict1:
dict1[A[i]+B[j]] = 1
else:
dict1[A[i]+B[j]]+=1
for m in range(len(C)):
for n in range(len(D)):
if -(C[m]+D[n]) in dict1:
res+=dict1[-(C[m]+D[n])]
return res