# 四数之和
给定一个包含 n 个整数的数组 nums 和一个目标值 target，判断 nums 中是否存在四个元素 a，b，c 和 d ，使得 a + b + c + d 的值与 target 相等？找出所有满足条件且不重复的四元组。
注意：答案中不可以包含重复的四元组。
示例 1：
输入：nums = [1,0,-1,0,-2,2], target = 0
输出：[[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
示例 2：
输入：nums = [], target = 0
输出：[]
提示：
0 <= nums.length <= 200-109 <= nums[i] <= 109-109 <= target <= 109
## template
```python
class Solution(object):
def fourSum(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[List[int]]
"""
nums.sort()
results = []
N = len(nums)
i = 0
while i < N-3:
if i > 0 and nums[i] == nums[i-1]:
i += 1
continue
j = i+1
while j < N-2:
if j > i+1 and nums[j] == nums[j-1]:
j += 1
continue
k = j+1
l = N-1
while k < l:
if k > j+1 and nums[k] == nums[k-1]:
k += 1
continue
while k < l and (target - nums[i] - nums[j] - nums[k] - nums[l]) < 0:
l -= 1
if k >= l:
break
if target == nums[i] + nums[j] + nums[k] + nums[l]:
results.append([
nums[i],
nums[j],
nums[k],
nums[l]
])
k += 1
j += 1
i += 1
return results
# %%
s = Solution()
print(s.fourSum(nums = [1,0,-1,0,-2,2], target = 0))
```
## 答案
```python
```
## 选项
### A
```python
```
### B
```python
```
### C
```python
```