Create 4Sum II.py

Author: sugia

4Sum II.py

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+'''
+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:
+1. (0, 0, 0, 1) -> A[0] + B[0] + C[0] + D[1] = 1 + (-2) + (-1) + 2 = 0
+2. (1, 1, 0, 0) -> A[1] + B[1] + C[0] + D[0] = 2 + (-1) + (-1) + 0 = 0
+'''
+
+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
+        """
+        box = {}
+        for a in A:
+            for b in B:
+                tmp = - a - b
+                if tmp in box:
+                    box[tmp] += 1
+                else:
+                    box[tmp] = 1
+                
+        res = 0
+        for c in C:
+            for d in D:
+                tmp = c + d
+                if tmp in box:
+                    res += box[tmp]
+        return res