18. 4Sum

这题和15题算法基本一模一样

code

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        sort(nums.begin(),nums.end());
        vector<vector<int>> res;
        if(nums.size()<4)
            return res;
        for(int i=0;i<nums.size()-3;++i){
            for(int j=i+1;j<nums.size()-2;++j){
                int sum=target-nums[i]-nums[j];
                int left=j+1,right=nums.size()-1;
                while(left<right){
                    if(nums[left]+nums[right]==sum){
                    //cout<<left<<' '<<right<<';';
                
                        res.push_back({nums[i],nums[j],nums[left],nums[right]});
                        while(nums[left+1]==nums[left])
                            left++;
                        while(nums[right-1]==nums[right])
                            right--;
                    }
                    if(nums[left]+nums[right]>sum)
                        right--;
                    else
                        left++;
                    //cout<<left<<' '<<right<<';';
                }
                while(j<nums.size()-2&&nums[j+1]==nums[j])
                    j++;
            }
            while(i<nums.size()-3&&nums[i+1]==nums[i])
                    i++;
        }
        return res;
    }
};