15.py

'''
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]
]


'''
class Solution(object):
    def threeSum(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        result = []
        nums.sort()
        l = len(nums)
        for i in range(0, l): 
          if i != 0 and nums[i] == nums[i-1]:
            continue

          j = i + 1
          k = l - 1

          while j < k:
            sum = nums[i] + nums[j] + nums[k]
            if sum < 0:
                j = j +1
            elif sum > 0:
                k = k - 1
            else:
              result.append([nums[i],nums[j], nums[k]])
              j = j + 1

              while j < k and nums[j] == nums[j-1]:
                j = j + 1

         
        return result