LeetCode18. 四数之和

class Solution { public: vector<vector<int>> fourSum(vector<int>& nums, int target) { int n = nums.size(); vector<vector<int>> ans; if (n < 4) { return ans; } sort(nums.begin(), nums.end()); for (int first = 0; first < n - 3; first++) { if (first > 0 && nums[first] == nums[first - 1]) { continue; } for (int second = first + 1; second < n - 2; second++) { if (second > first + 1 && nums[second] == nums[second - 1]) { continue; } int third = second + 1, fourth = n - 1; while (third < fourth) { if (third > second + 1 and nums[third] == nums[third - 1]) { third++; continue; } if (fourth < n - 1 && nums[fourth] == nums[fourth + 1]) { fourth--; continue; } if (nums[first] + nums[second] + nums[third] + nums[fourth] == target) { ans.push_back({ nums[first], nums[second], nums[third], nums[fourth] }); third++; fourth--; } else if (nums[first] + nums[second] + nums[third] + nums[fourth] > target) { fourth--; } else { third++; } } } } return ans; } };