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]
]

解析

此題找出所有三個數字之和為0的不同解。

解法

class Solution:
    def threeSum(self, nums):
        res = []
        nums.sort()
        if len(nums) < 3:
            return res

        for i in range(len(nums) - 2):
            if i > 0 and nums[i] == nums[i-1]:
                continue
            l, r = i + 1, len(nums) - 1
            while l < r:
                s = nums[i] + nums[l] + nums[r]
                if s == 0:
                    res.append([nums[i], nums[l], nums[r]])
                    l += 1
                    r -= 1
                    while l < r and nums[l] == nums[l - 1]:
                        l += 1
                    while l < r and nums[r] == nums[r + 1]:
                        r -= 1
                elif s < 0:
                    l += 1
                else:
                    r -= 1
        return res

備註

希望透過記錄解題的過程，可以對於資料結構及演算法等有更深一層的想法。
如有需訂正的地方歡迎告知，若有更好的解法也歡迎留言，謝謝。