力扣18. 四数之和

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        vector<vector<int>> result;
        sort(nums.begin(), nums.end());
        for(int k = 0; k < nums.size(); k++) {
            if(nums[k] > target && nums[k] >= 0) break;
            if(k > 0 && nums[k - 1] == nums[k]) continue;
            for(int i = k + 1; i < nums.size(); i++) {
                if(nums[k] + nums[i] > target && nums[k] + nums[i] >= 0) break;
                if(i > k + 1 && nums[i - 1] == nums[i]) continue;
                int left = i + 1;
                int right = nums.size() - 1;
                while(left < right) {
                    long long sum = (long long)nums[k] + nums[i] + nums[left] + nums[right];
                    if(sum > target) right--;
                    else if(sum < target) left++;
                    else{
                        result.push_back({nums[k], nums[i], nums[left++], nums[right--]});
                        while(left < right && nums[left - 1] == nums[left]) left++;
                        while(left < right && nums[right + 1] == nums[right]) right--;
                    }
                }
            }
        }

        return result;
    }
};