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: 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] ] class Solution { public: //int threeSumClosest(vector<int>& nums, int target) vector<vector<int>> fourSum(vector<int>& nums, int target) { sort(nums.begin(), nums.end()); vector<vector<int>> foursum; vector<int> sum; if (nums.empty()) return foursum; int mini = nums[0] + nums[1] + nums[2] + nums[3]; for (int i = 0; i < nums.size()-3; i++) { if (i != 0 && nums[i] > target&& nums[i]>0) break; if (i != 0 && nums[i] == nums[i - 1]) continue; for (int j = i + 1; j < nums.size()-2; j++) { if (j > i + 1 && nums[j] == nums[j - 1]) continue; if (nums[i] + nums[j] > target&&nums[j]>0) break; int left = j + 1, right = nums.size() - 1; int sums = nums[i] + nums[j]; while (left < right) { if (sums + nums[left] + nums[right] == target) { sum.push_back(nums[i]); sum.push_back(nums[j]); sum.push_back(nums[left]); sum.push_back(nums[right]); foursum.push_back(sum); sum.clear(); while (nums[left + 1] == nums[left]) left++; left++; } else if (sums + nums[left] + nums[right] < target) { left++; } else { right--; } } } } return foursum; } };
