3Sum

[leeway00]

  def threeSum(self, nums: List[int]) -> List[List[int]]:
      result = []
      nums.sort()
      for i in range(len(nums)-2):
          if i>0 and nums[i] == nums[i-1]:
              continue
          left, right = i+1, len(nums)-1
          while left < right:
              summ = nums[i] + nums[left] +nums[right]
              if summ <0:
                  left +=1
              elif summ >0:
                  right -=1
              else:
                  result.append([nums[i], nums[left], nums[right]])

                  while left < right and nums[left] == nums[left+1]:
                      left +=1
                  while left < right and nums[right]==nums[right-1]:
                      right -=1
                  left+=1
                  right -=1
      return result

[leeway00]

This is slower

    def threeSum(self, nums: List[int]) -> List[List[int]]:
        n = len(nums)
        if n<3:
            return []

        nums = sorted(nums)
        twosum = defaultdict(int)
        for i, j in combinations([*range(len(nums)-1)], 2):
            if (nums[i], nums[j]) not in twosum:
                twosum[(nums[i],nums[j])] = j
        reverted = defaultdict(int)
        for ind, val in enumerate(nums):
            reverted[val] = max(ind, reverted[val])

        ans = []
        for val, ind in twosum.items():
            if reverted[-sum(val)] > ind:
                ans.append([val[0], val[1], -sum(val)])
        return ans