Leetcode 15. 3Sum

https://leetcode.com/problems/3sum/

Sort the array, select one number, and then approach the sum from both sides.

Solution:

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

Run Time: 212 ms