3Sum

06/25/2016 Array Two Pointers

Question

Given an array S of n integers, are there elements a, b, c in S 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.

For example, given array S = [-1, 0, 1, 2, -1, -4],

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

Solution

Result: Accepted Time: 56ms

Here should be some explanations.

话说这题在知乎上还火了一下。第22期职人介绍所中，有让赵劼和winter现场撸这题，不过表现不尽如人意啊！

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        vector<vector<int>> ret;
        const int n = nums.size();

        sort(nums.begin(), nums.end());
        for (int i = 0; i < n-2; ++i)
        {
            if (nums[i] > 0)
                break;
            if (i != 0 && nums[i] == nums[i-1])
                continue;

            int target = 0 - nums[i];
            int left = i + 1;
            int right = n - 1;

            while (left < right)
            {
                if (nums[right] < 0)
                    break;
                if ((nums[left] + nums[right]) == target)
                    ret.push_back(vector<int>{nums[i],nums[left],nums[right]});

                if ((nums[left] + nums[right]) < target)
                {
                    ++left;
                     while (left < right && nums[left-1] == nums[left]) ++left;

                }
                else
                {
                    --right;
                    while (left < right && nums[right+1] == nums[right]) --right;
                }
            }
        }
        return ret;
    }
};

Complexity Analytics

  • Time Complexity:
  • Space Complexity: