LeetCode: 3Sum

class Solution {
public:

    using pi = pair <int, int>;
    vector < vector <int>> ans;
    int pos[200010], neg[200010], zero;
    pi piz = {0, 0};

    vector<vector<int>> threeSum(vector<int>& nums) {
        int len = nums.size();

        if(len < 3) return ans;

        sort(nums.begin(), nums.end());

        for(auto i: nums){
            if(i == 0) zero ++;
            else if(i > 0) pos[i] ++;
            else neg[-i] ++;
        }

        for(int i=0;i<len;i++){
            for(int j=i+1;j<len;j++){
                int a = nums[i], b = nums[j], c = a + b;
                if(a < 0 and b < 0 and pos[-c] != 0){
                    ans.push_back({a, b, -c});
                }
                if(a > 0 and b > 0 and neg[c] != 0){
                    ans.push_back({-c, a, b});
                }
            }
        }

        if(zero >= 1){
            for(int i=1;i<=100000;i++){
                if(pos[i] != 0 and neg[i] != 0)
                    ans.push_back({-i, 0, i});
            }
        }

        if(zero >= 3) ans.push_back({0, 0, 0});

        sort(ans.begin(), ans.end());

        ans.resize( unique(ans.begin(), ans.end()) - ans.begin() );

        return ans;
    }
};