class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        // The main issue is to remove duplicate answers
        int n = nums.size();
        sort(nums.begin(), nums.end());
        vector<vector<int>> ret;
        int preid = -1;
        for(int i = 0; i < n; i++){
            if(preid != -1 && nums[i] == nums[preid]) continue;
            int l = i + 1, r = n - 1;
            while(l < r){
                int sum = nums[i] + nums[l] + nums[r];
                if(sum == 0){
                    ret.push_back({nums[l], nums[r], nums[i]});
                    int tmp = nums[l];
                    while(l < r && nums[l] == tmp) l++;
                    preid = i;
                }else if(sum > 0){
                    r--;
                }else{
                    l++;
                }
            }
        }
        return ret;
    }
};