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;
}
};