Merge pull request #185 from tw2665/patch-1

添加 0454.四数相加II python版本

problems/0454.四数相加II.md

@@ -121,6 +121,37 @@ class Solution {
 
 Python：
 
+```
+class Solution(object):
+    def fourSumCount(self, nums1, nums2, nums3, nums4):
+        """
+        :type nums1: List[int]
+        :type nums2: List[int]
+        :type nums3: List[int]
+        :type nums4: List[int]
+        :rtype: int
+        """
+        # use a dict to store the elements in nums1 and nums2 and their sum
+        hashmap = dict()
+        for n1 in nums1:
+            for n2 in nums2:
+                if n1 + n2 in hashmap:
+                    hashmap[n1+n2] += 1
+                else:
+                    hashmap[n1+n2] = 1
+        
+        # if the -(a+b) exists in nums3 and nums4, we shall add the count
+        count = 0
+        for n3 in nums3:
+            for n4 in nums4:
+                key = - n3 - n4
+                if key in hashmap:
+                    count += hashmap[key]
+        return count
+                
+
+```
+
 
 Go：