Given four lists A, B, C, D of integer values, compute how many tuples (i, j, k, l) there are such that A[i] + B[j] + C[k] + D[l] is zero.
To make problem a bit easier, all A, B, C, D have same length of N where 0 ≤ N ≤ 500. All integers are in the range of -228 to 228 - 1 and the result is guaranteed to be at most 231 - 1.
Example:
Input:
A = [ 1, 2]
B = [-2,-1]
C = [-1, 2]
D = [ 0, 2]
Output:
2
Explanation:
The two tuples are:
- (0, 0, 0, 1) -> A[0] + B[0] + C[0] + D[1] = 1 + (-2) + (-1) + 2 = 0
- (1, 1, 0, 0) -> A[1] + B[1] + C[0] + D[0] = 2 + (-1) + (-1) + 0 = 0
class Solution:
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
"""
dic1,dic2 = {},{}
for i in A:
for j in B:
if i+j not in dic1:
dic1[i+j] = 1
else:
dic1[i+j] += 1
for i in C:
for j in D:
if i+j not in dic2:
dic2[i+j] = 1
else:
dic2[i+j] += 1
res = 0
for key,value in dic1.items():
if -key in dic2:
res += value*dic2[-key]
return res
两个两个地处理，把结果保存在字典中。