15. 三数之和(双指针)

给你一个包含 n 个整数的数组 nums,判断 nums 中是否存在三个元素 a,b,c ,使得 a + b + c = 0 ?请你找出所有和为 0 且不重复的三元组。

注意:答案中不可以包含重复的三元组。

 

示例 1:

输入:nums = [-1,0,1,2,-1,-4]
输出:[[-1,-1,2],[-1,0,1]]
示例 2:

输入:nums = []
输出:[]
示例 3:

输入:nums = [0]
输出:[]
 

提示:

0 <= nums.length <= 3000
-105 <= nums[i] <= 105

来源:力扣(LeetCode)
链接:https://leetcode-cn.com/problems/3sum
著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        int len = nums.size();
        vector<vector<int>> res;
        if(len < 3)
        {
            return res;
        }
        sort(nums.begin(), nums.end());
        const int target = 0;
        for(int first = 0; first< len; first++)
        {
            if(first > 0 && nums[first] == nums[first-1])
            {
                continue;
            }
            int third = len-1;
            for(int second = first +1; second < third; second++)
            {
                if(second > first+1 && nums[second] == nums[second - 1])
                {
                    continue;
                }
                while(third > second && nums[first] + nums[second] + nums[third] > target)
                {
                    third--;
                }
                if(second < third && (nums[first] + nums[second] + nums[third]  == 0))
                {
                    vector<int> tmp ;
                    tmp.push_back(nums[first]);
                    tmp.push_back(nums[second]);
                    tmp.push_back(nums[third]);
                    res.push_back(tmp);
                }

            }
        }
    return res;
    }
};

  

posted @ 2021-06-27 14:44  linqiaozhou  阅读(34)  评论(0编辑  收藏  举报