LeetCode 15. 3Sum

题目

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]
]

思路

Two-Pointers.

代码

class Solution(object):
    def threeSum(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        N = len(nums)
        nums.sort()
        res = []
        for t in range(N - 2):
            if t > 0 and nums[t] == nums[t - 1]:
                    continue
            i, j = t + 1, N - 1
            while i < j:
                _sum = nums[t] + nums[i] + nums[j]
                if _sum == 0:
                    res.append([nums[t], nums[i], nums[j]])
                    i += 1
                    j -= 1
                    while i < j and nums[i] == nums[i - 1]:
                        i += 1
                    while i < j and nums[j] == nums[j + 1]:
                        j -= 1
                elif _sum < 0:
                    i += 1
                else:
                    j -= 1
        return res