3 sum with 2 pointers without hashmap

3sum_2pointers.py

class Solution:
    # two-pointer solution
    def threeSum(self, nums: list[int]) -> list[int]:
        nums.sort()

        seen = set()
        len_nums = len(nums)

        result_triplets = []

        for i in range(len_nums):
            num = nums[i]
            
            # de-duplicate
            if num in seen:
                continue
            seen.add(num)

            left = i + 1
            right = len_nums - 1

            pairs_seen = set()
            # since array is sorted, as long as we format our pairs as: (nums_left, nums_right)
            # they will be sorted and unique 

            while left < right:
                nums_left = nums[left]
                nums_right = nums[right]

                curr_sum = num + nums_left + nums_right
                if curr_sum == 0:
                    if (nums_left, nums_right) in pairs_seen:
                        # i wonder if we could do right -= 1 instead?
                        # yes, it still works
                        left += 1
                        continue
                    pairs_seen.add((nums_left, nums_right))
                    result_triplets.append([num, nums_left, nums_right])
                elif curr_sum < 0:
                    # since `nums` is sorted, incrementing left helps us raise curr_sum towards 0
                    left += 1
                    continue
                else:
                    # since `nums` is sorted, decrementing right helps us lower curr_sum towards 0
                    right -= 1
                    continue

        return result_triplets