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;
}
};