# 4Sum

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

Note:

The solution set must not contain duplicate quadruplets.

Example:

Given array nums = [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]
]```

Solution in C++

```class Solution {
public:
vector<vector<int>> fourSum(vector<int>& nums, int target) {
sort(nums.begin(), nums.end());

map<int,int> mp;
for(int i=0; i<nums.size(); i++) mp[nums[i]]=i+1;

set<vector<int>> sRet; // storage will contain results

for(int i=0; i<nums.size(); i++)
for(int j=i+1; j<nums.size(); j++)
for(int k=j+1; k<nums.size(); k++) {
int l = target - nums[i] - nums[j] - nums[k];
if (mp[l] && (mp[l]-1)>k) {
vector<int> tmp = {nums[i], nums[j], nums[k], l};
sRet.insert(tmp);
}
}
vector<vector<int>> ret;
for(auto n:sRet) ret.push_back(n);
return ret;
}
};```
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