Leetcode/4sum.cpp at main · Pradumnk23/Leetcode · GitHub

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class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        vector<vector<int>> res;
        if(nums.empty())
            return res;
        int n=nums.size();
        sort(nums.begin(), nums.end());

        for(int i=0; i<n; i++)
        {
            for(int j=i+1; j<n; j++)
            {
                int target2=target-nums[i]-nums[j];
                int left=j+1;
                int right=n-1;
                while(left<right)
                {
                    int twosum=nums[left]+nums[right];
                    if(twosum<target2)
                        left++;
                    else if(twosum>target2)
                        right--;
                    else
                    {
                        vector<int>quad(4,0);
                        quad[0]=nums[i];
                        quad[1]=nums[j];
                        quad[2]=nums[left];
                        quad[3]=nums[right];
                        res.push_back(quad);
                        while(left<right && nums[left]==quad[2])
                            left++;
                        while(left<right && nums[right]==quad[3])
                            right--;
                    }
                }
                while(j+1<n && nums[j+1]==nums[j])
                    j++;
            }
            while(i+1<n && nums[i+1]==nums[i])
                    i++;
        }

        return res;
    }
};