题解 | #四数之和#

class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param nums int整型vector 
     * @param target int整型 
     * @return int整型vector<vector<>>
     */
    vector<vector<int> > fournumber(vector<int>& nums, int target) {
        // write code here
        vector<vector<int>> tmp;
        sort(nums.begin(),nums.end());
        int n = nums.size();
        for(int i = 0;i<n;)
        {
            //固定第一个数
            int p1 = nums[i];
            for(int j = i+1;j< n-1;)
            {
                int p2 = nums[j];
                int left = j+1;
                int right = n-1;
                while(left < right)
                {
                    if(nums[left] + nums[right] > ((long long)target - p1 -p2)) --right;
                    else if(nums[left] + nums[right] < ((long long)target - p1 -p2)) ++left;
                    else
                  {
                      tmp.push_back({p1,p2,nums[left],nums[right]});
                      ++left,--right;//保证遍历充分
                      while(left < right && nums[left] == nums[left-1])  ++left;//去重操作
                      while(right > left && nums[right] == nums[right+1]) --right;
                  }
                }
                j++;
                while(j < n-1 && nums[j] == nums[j-1])   ++j;
            }
            i++;
            while(i<n && nums[i] == nums[i-1])   ++i;
        }
        return tmp;
    }
};