3Sum.cpp

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        vector<vector<int>> ans;
        if(nums.size()<=2){
            return ans;
        }
        vector<int> v;
        sort(nums.begin(),nums.end());
        for(int i=0;i<nums.size()-2;i++){
            if(i==0 || (i>0 && nums[i]!=nums[i-1])){
                int low=i+1;
                int high=nums.size()-1;
                int sum=0-nums[i];
                while(low<high){
                    if(nums[low]+nums[high]==sum){
                        v.push_back(nums[i]);
                        v.push_back(nums[low]);
                        v.push_back(nums[high]);
                        ans.push_back(v);
                        v.clear();
                        while(low<high && nums[low]==nums[low+1]) low++;
                        while(low<high && nums[high]==nums[high-1]) high--;
                        low++;
                        high--;
                    }
                    else if(nums[low]+nums[high]>sum){
                        high--;
                    }else{
                        low++;
                    }
                }
            }
        }
        return ans;
    }
};