but the run time is slow, 564 ms. plz tell me how to improve! thx

```
def twoSum(self, nums, target):
sol = set()
n_set = set()
for num in nums:
if num in n_set:
tup = tuple( sorted([num, target-num, -target]) )
sol.add(tup)
n_set.add(target - num)
return sol
def threeSum(self, nums):
sol = set()
for i, n in enumerate(nums):
sol = sol.union( self.twoSum(nums[i+1:], -n) )
return list(sol)
```