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

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

 1 #include <iostream>
 2 #include <queue>
 3 #include <vector>
 4 using namespace std;
 5 struct Node
 6 {
 7     int v;
 8     Node *l, *r;
 9     Node(int a = -1) :v(a), l(nullptr), r(nullptr) {}
10 };
11 Node* root = nullptr;
12 int n, level = -1, a;
13 vector<int>res;
14 void creatTree(Node*& root, int x)
15 {
16     if (root == nullptr)
17     {
18         root = new Node(x);
19         return;
20     }
21     if (x <= root->v)
22         creatTree(root->l, x);
23     else
24         creatTree(root->r, x);
25 }
26 void BFS(Node* root)
27 {
28     queue<Node*>q;
29     q.push(root);
30     while (!q.empty())
31     {
32         int num = 0;
33         queue<Node*>temp;
34         while (!q.empty())
35         {
36             Node* p = q.front();
37             q.pop();
38             num++;
39             if (p->l != nullptr)
40                 temp.push(p->l);
41             if (p->r != nullptr)
42                 temp.push(p->r);
43         }
44         q = temp;
45         res.push_back(num);
46     }
47 }
48 int main()
49 {
50 
51     cin >> n;
52     while (n--)
53     {
54         cin >> a;
55         creatTree(root, a);
56     }
57     BFS(root);
58     cout << res[res.size() - 1] << " + " << res[res.size() - 2] << " = " << res[res.size() - 1] + res[res.size() - 2] << endl;
59     return 0;
60 }