3sum

class Solution(object):
    def threeSum(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        if len(nums)<3:
            return []
        res = {}
        sol = []
        flag = [0]*len(nums)
        nums.sort()
        for i in range(len(nums)):
            j = i + 1
            k = len(nums)-1
            while j<k:
                if nums[j]+nums[k]+nums[i] > 0:
                    k-=1
                elif nums[j]+nums[k]+nums[i] < 0:
                    j+=1
                else:
                    res[nums[i], nums[j], nums[k]] = 0
                    flag[i], flag[j], flag[k] = 1, 1, 1
                    j+=1
        for i in res:
            sol.append(list(i))
        return sol   #convert to set