class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
      vector<vector<int>> result;
        sort(nums.begin() , nums.end());
        for (int i = 0; i < nums.size(); i++)
        {
            if (nums[i] > target && target>=0) return result;//减枝，当target大于0，第一个值大于target时，认为无效直接返回
            for (int j = i + 1; j < nums.size(); j++)
            {
                int left = j + 1;
                int right = nums.size() - 1;
                while (left < right)
                {
                    if (((long)nums[i] + nums[j] + nums[left] + nums[right]) == target)//要转换成long 要不会溢出
                    {
                        if(find(result.begin() , result.end() , vector<int>{nums[i], nums[j], nums[left], nums[right]})==result.end() )
                             result.push_back(vector<int>{nums[i],nums[j],nums[left],nums[right]});
                        while (left < right && nums[left] == nums[left + 1]) left++;
                        while (left < right && nums[right] == nums[right - 1]) right--;
                        left++;
                        right--;
                    }else if((long)nums[i] + nums[j] + nums[left] + nums[right] > target) right--;
                    else left++;
                }
            }
        }
        return result;
    }
};

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++) {
            // 剪枝处理
            if (nums[k] > target && nums[k] >= 0) {
              break; // 这里使用break，统一通过最后的return返回
            }
            // 对nums[k]去重
            if (k > 0 && nums[k] == nums[k - 1]) {
                continue;
            }
            for (int i = k + 1; i < nums.size(); i++) {
                // 2级剪枝处理
                if (nums[k] + nums[i] > target && nums[k] + nums[i] >= 0) {
                    break;
                }
                // 对nums[i]去重
                if (i > k + 1 && nums[i] == nums[i - 1]) {
                    continue;
                }
                int left = i + 1;
                int right = nums.size() - 1;
                while (right > left) {
                    // nums[k] + nums[i] + nums[left] + nums[right] > target 会溢出
                    if ((long) nums[k] + nums[i] + nums[left] + nums[right] > target) {
                        right--;
                    // nums[k] + nums[i] + nums[left] + nums[right] < target 会溢出
                    } else if ((long) nums[k] + nums[i] + nums[left] + nums[right]  < target) {
                        left++;
                    } else {
                        result.push_back(vector<int>{nums[k], nums[i], nums[left], nums[right]});
                        // 对nums[left]和nums[right]去重
                        while (right > left && nums[right] == nums[right - 1]) right--;
                        while (right > left && nums[left] == nums[left + 1]) left++;
                        // 找到答案时，双指针同时收缩
                        right--;
                        left++;
                    }
                }
            }
        }
        return result;
    }
};

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