Commite1bbd30

borninfreedom

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update 四数相加II，添加了一个更加简洁的python代码

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+25

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Lines changed: 25 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -120,7 +120,7 @@ class Solution {`
`120`	`120`
`121`	`121`	`Python：`
`122`	`122`
`123`		-```
	`123`	+```python
`124`	`124`	`classSolution(object):`
`125`	`125`	`deffourSumCount(self,nums1,nums2,nums3,nums4):`
`126`	`126`	`"""`
`@@ -147,7 +147,31 @@ class Solution(object):`
`147`	`147`	`if keyin hashmap:`
`148`	`148`	`count+= hashmap[key]`
`149`	`149`	`return count`
	`150`	`+`
	`151`	`+# 下面这个写法更为简洁，但是表达的是同样的算法`
	`152`	`+# class Solution:`
	`153`	`+# def fourSumCount(self, nums1: List[int], nums2: List[int], nums3: List[int], nums4: List[int]) -> int:`
	`154`	`+# from collections import defaultdict`
	`155`	`+`
	`156`	`+# hashmap = defaultdict(int)`
	`157`	`+`
	`158`	`+# for x1 in nums1:`
	`159`	`+# for x2 in nums2:`
	`160`	`+# hashmap[x1+x2] += 1`
	`161`	`+`
	`162`	`+# count=0`
	`163`	`+# for x3 in nums3:`
	`164`	`+# for x4 in nums4:`
	`165`	`+# key = -x3-x4`
	`166`	`+# value = hashmap.get(key)`
	`167`	`+`
	`168`	`+# dict的get方法会返回None（key不存在）或者key对应的value`
	`169`	`+# 所以如果value==0，就会继续执行or，count+0，否则就会直接加value`
	`170`	`+# 这样就不用去写if判断了`
	`171`	`+`
	`172`	`+# count += value or 0`
`150`	`173`
	`174`	`+# return count`
`151`	`175`
`152`	`176`	```
`153`	`177`

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