3Sum.cpp

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
            sort(nums.begin(), nums.end());
            vector<vector<int>> ans;
            for(int i = 0; i<nums.size(); i++){
                if(i>0 && nums[i] == nums[i-1]) continue;
                int j = i+1;
                int k = nums.size() - 1;

                while(j<k){
                    int sum = nums[i] + nums[j] + nums[k];
                    if(sum<0){
                        j++;
                    }
                    else if(sum > 0){
                        k--;
                    }
                    else{
                        vector<int> temp = {nums[i], nums[j], nums[k]};
                        ans.push_back(temp);
                        j++;
                        k--;
                        while( j<k && nums[j] == nums[j-1]) j++;
                        while( j<k && nums[k] == nums[k+1]) k--;
                    }
                }
            }
            return ans;
        }
};