Create 4sum-ii.py

Author: kamyu104

Python/4sum-ii.py

@@ -0,0 +1,37 @@
+# Time:  O(n^2)
+# Space: O(n^2)
+
+# 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
+        """
+        A_B_sum = collections.Counter(a+b for a in A for b in B)
+        return sum(A_B_sum[-c-d] for c in C for d in D)