15. 3Sum

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note:

The solution set must not contain duplicate triplets.

Example:

Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
  [-1, 0, 1],
  [-1, -1, 2]
]

    def threeSum(nums):
        n = len(nums)
        res = set()
        nums.sort()

        if n < 3:
            return []

        for i in range(n - 2):
            if i == 0 or nums[i] != nums[i - 1]:
                j = i + 1
                k = n - 1

                while j < k:
                    sum = nums[i] + nums[j] + nums[k]

                    if sum == 0:
                        res.add((nums[i], nums[j], nums[k]))
                        j += 1
                        k -= 1
                    elif sum < 0:
                        j += 1
                    else:
                        k -= 1
        return list(res)


nums = [-1, 0, 1, 2, -1, -4]
print(threeSum(nums))