leetcode:4Sum [18]

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;}};