LeetCode - 3Sum

The problem is described as following:

Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
Note:
- Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
- The solution set must not contain duplicate triplets.
For example, given array S = {-1 0 1 2 -1 -4},
A solution set is:
(-1, 0, 1)
(-1, -1, 2)

My solution is as following:

class Solution:    # @return a list of lists of length 3, [[val1,val2,val3]]    def threeSum(self, num):        i, num, result = 0, sorted(num), []        while i < len(num)-2:            j, k = i+1, len(num)-1            while j < k:                if num[i] + num[j] + num[k] < 0:                    j += 1                elif num[i] + num[j] + num[k] > 0:                    k -= 1                else:                    result.append((num[i], num[j], num[k]))                    j, k = j+1, k-1                    while j < k and num[j] == num[j-1]:                        j += 1                    while j < k and num[k] == num[k+1]:                        k -= 1            i += 1            while i < len(num)-1 and num[i] == num[i-1]:                i += 1        return result

这里要注意的是首先通过排序来使查找更高效，每次找到可行解之后要为避免重复而进行重复元素的过滤。