3Sum.cpp

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