Leetcode-15-三数之和

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 ？请你找出所有满足条件且不重复的三元组。

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

        }
        return ans;
    }
};