# sort and then use two pointers. avoiding duplicates was the real hassle. difficult implementation

class Solution:
    def threeSum(self, nums: List[int]) -> List[List[int]]:

        nums.sort()
        result = []
        nums = list(set(nums))

        for index, num in enumerate(nums):

            # not needed, it's optimisation over the current approach to save
            # some computation time
            if num > 0:
                break

            # avoid duplicates
            if index!=0 and nums[index] == nums[index-1]:
                continue

            target = -num

            start = index + 1
            end = len(nums) - 1

            while(start < end):

                if nums[start] + nums[end] < target:
                    start = start + 1
                elif nums[start] + nums[end] > target:
                    end = end - 1
                else:
                    result.append([nums[index], nums[start], nums[end]])
                    start = start + 1
                    end = end - 1

                    while(start < end and nums[start] == nums[start-1]):
                        start = start + 1

                    while(start < end and nums[end] == nums[end+1]):
                        end = end - 1

        return result