three_sum.cpp

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) 
    {
        if(nums.size() < 3)return {};
        vector<vector<int>> res;
        sort(nums.begin(),nums.end());
        int low,high,sum;
        for(int i = 0; i < nums.size()-2; i++)
        {
            if(i == 0 || (i>0 && nums[i] != nums[i-1]))
            {
                low = i+1;
                high = nums.size()-1;
                sum = 0-nums[i];
                while(low < high)
                {
                    if(nums[low]+nums[high] == sum)
                    {
                        res.push_back({nums[low],nums[high],nums[i]});
                        while(low<high && nums[low] == nums[low+1])low++;
                        while(low<high && nums[high] == nums[high-1])high--;
                        low++; high--;
                    }
                    else if(nums[low]+nums[high] < sum)low++;
                    else high--;
                }
            }
        }
        return res;
    }
};