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

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

先排序，再用三个指针协同操作，最后再考虑处理重复数据。

 1 class Solution:
 2     def threeSum(self, nums):
 3         """
 4         :type nums: List[int]
 5         :rtype: List[List[int]]
 6         """
 7         nums.sort()
 8         result = []
 9         for i in range(len(nums)-2):
10             if i > 0 and nums[i] == nums[i-1]:
11                 continue
12             left, right = i + 1, len(nums) - 1
13             while left < right :
14                 sum = nums[i] + nums[left] + nums[right]
15                 if sum < 0 :
16                     left += 1
17                 elif sum > 0 :
18                     right -= 1
19                 else :
20                     result.append([nums[i], nums[left], nums[right]])
21                     while left < right and nums[left] == nums[left + 1]:
22                         left += 1
23                     while left < right and nums[right] == nums[right - 1]:
24                         right -= 1
25                     left += 1
26                     right -= 1
27         return result