3Sum

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        
      vector<vector<int>> ans;
        sort(nums.begin(),nums.end());
        int n =nums.size();
        for(int i=0;i<n;i++)
        {
            int a = nums[i];
            int t=-a;
            int s=i+1,e=n-1;
            while(s<e)
            {
                if(nums[s]+nums[e]==t)
                {
                    ans.push_back({nums[i],nums[s],nums[e]});
                    while(s<e && nums[s]==nums[s+1]) s++;
                    while(s<e && nums[e]==nums[e-1]) e--;
                    s++;
                    e--;
                }
                else if(nums[s]+nums[e]>t)
                {
                    e--;
                }
                else
                {
                    s++;
                }
            }
            while(i+1<n && nums[i+1]==nums[i]) i++;
        }
        return ans;
        
    }
};