3Sum

#define vi(x) vector<x>
class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        vi(vi(int)) out;
        if(nums.size()<=2) return out; 
        sort(nums.begin(), nums.end());
        int frst = 0, secnd = 1, third = nums.size()-1;
        for(;frst< nums.size()-2; frst++)
        {
            while(frst != 0 && frst < nums.size() && nums[frst-1]==nums[frst]) frst++;
            secnd = frst+1;third = nums.size()-1;
            while(secnd < third)
            {
                if(nums[frst]+nums[secnd]+nums[third] == 0)
                {
                    out.push_back(vi(int){nums[frst], nums[secnd], nums[third]});
                    secnd++;
                    while(secnd < nums.size() && nums[secnd-1] == nums[secnd]) secnd++;
                }
                else if(nums[frst]+nums[secnd]+nums[third] < 0)
                {
                    secnd++;
                }
                else
                {
                    third--;
                }
            }
        }
        return out;
    }
};