LeetCode 18 4Sum

18. 4Sum

Total Accepted: 68829 Total Submissions: 291751 Difficulty: Medium

Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Note:

• Elements in a quadruplet (a,b,c,d) must be in non-descending order. (ie, a ≤ b ≤ c ≤ d)
• The solution set must not contain duplicate quadruplets.

    For example, given array S = {1 0 -1 0 -2 2}, and target = 0.

    A solution set is:
    (-1,  0, 0, 1)
    (-2, -1, 1, 2)
    (-2,  0, 0, 2)

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找4个数，加起来等于target.

还是一样的方法

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) 
    {
        set<vector<int>> vis;
        vector<vector<int>> ret;
        int len=nums.size();
        sort(nums.begin(),nums.end());
        for(int i=0;i<len;i++)
                for(int j=i+1;j<len;j++)
                {
                        int l=j+1,r=len-1;
                        while(l<r)
                        {
                                int temp=nums[i]+nums[j]+nums[l]+nums[r];
                                if(temp==target)
                                {
                                        vector<int> cur;
                                        cur.push_back(nums[i]);
                                        cur.push_back(nums[j]);
                                        cur.push_back(nums[l]);
                                        cur.push_back(nums[r]);
                                        vis.insert(cur);
                                        l++;
                                        r--;
                                }
                                else if(temp<target)
                                        l++;
                                else
                                        r--;
                        }
                }
		for(set<vector<int>>::iterator it = vis.begin(); it != vis.end(); it++)
			ret.push_back(*it);
        return ret;
    }
};