- 4Sum Medium
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Share Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.
Note:
The solution set must not contain duplicate quadruplets.
Example:
Given array nums = [1, 0, -1, 0, -2, 2], and target = 0.
A solution set is: [ [-1, 0, 0, 1], [-2, -1, 1, 2], [-2, 0, 0, 2] ]
思路：双指针，先定a,b两个数，nTarget=target-a-b 后面c=nums[b+1],d=nums[len(nums)-1], 如果c+d==nTarget,添加进set 如果c+d>nTArget,d往前进一位 如果c+d<nTArget,c往后进一位 注意去重，我这边为set加元组去重
代码：python3
class Solution:
def fourSum(self, nums, target) :
nums=sorted(nums)
s=set()
for x in range(0,len(nums)):
a=nums[x]
for y in range(x+1,len(nums)):
b=nums[y]
target1=target-a-b
i=y+1
j=len(nums)-1
while(i<j):
if nums[i]+nums[j]==target1:
s.add((nums[x],nums[y],nums[i],nums[j]))
i=i+1
j=j-1
elif nums[i]+nums[j]<target1:
i=i+1
else:
j=j-1
return list(s)
if __name__ == '__main__':
print(Solution().fourSum([-3,-2,-1,0,0,1,2,3],0))
