PAT甲级——A1115 Counting Nodes in a BST【30】

A Binary Search Tree (BST) is recursively defined as a binary tree which has the following properties:

• The left subtree of a node contains only nodes with keys less than or equal to the node's key.
• The right subtree of a node contains only nodes with keys greater than the node's key.
• Both the left and right subtrees must also be binary search trees.

Insert a sequence of numbers into an initially empty binary search tree. Then you are supposed to count the total number of nodes in the lowest 2 levels of the resulting tree.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤) which is the size of the input sequence. Then given in the next line are the N integers in [which are supposed to be inserted into an initially empty binary search tree.

Output Specification:

For each case, print in one line the numbers of nodes in the lowest 2 levels of the resulting tree in the format:

n1 + n2 = n

where n1 is the number of nodes in the lowest level, n2 is that of the level above, and n is the sum.

Sample Input:

9
25 30 42 16 20 20 35 -5 28

Sample Output:

2 + 4 = 6

 #include <iostream>
 #include <queue>
 #include <vector>
 using namespace std;
 struct Node
 {
     int v;
     Node *l, *r;
     Node(int a = -) :v(a), l(nullptr), r(nullptr) {}
 };
 Node* root = nullptr;
 int n, level = -, a;
 vector<int>res;
 void creatTree(Node*& root, int x)
 {
     if (root == nullptr)
     {
         root = new Node(x);
         return;
     }
     if (x <= root->v)
         creatTree(root->l, x);
     else
         creatTree(root->r, x);
 }
 void BFS(Node* root)
 {
     queue<Node*>q;
     q.push(root);
     while (!q.empty())
     {
         int num = ;
         queue<Node*>temp;
         while (!q.empty())
         {
             Node* p = q.front();
             q.pop();
             num++;
             if (p->l != nullptr)
                 temp.push(p->l);
             if (p->r != nullptr)
                 temp.push(p->r);
         }
         q = temp;
         res.push_back(num);
     }
 }
 int main()
 {

     cin >> n;
     while (n--)
     {
         cin >> a;
         creatTree(root, a);
     }
     BFS(root);
     cout << res[res.size() - ] << " + " << res[res.size() - ] << " = " << res[res.size() - ] + res[res.size() - ] << endl;
     return ;
 }