1115 Counting Nodes in a BST (30分)
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 (≤1000) which is the size of the input sequence. Then given in the next line are the N integers in [−1000,1000] 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<vector>
#include<algorithm>
using namespace std;
int n;
int num[1001]{ 0 };
int minx = -1;
struct info {int data;info* left;info* right;
};
void insert(info* &root, int value)
{if (!root){root = new info;root->data = value;root->left = nullptr;root->right = nullptr;return;}if (value <= root->data)insert(root->left, value);if (value > root->data)insert(root->right, value);
}
void dfs(info* root,int depth)
{if (!root)return;if (minx < depth){minx = depth;}num[depth]++;dfs(root->left, depth + 1);dfs(root->right, depth + 1);
}
int main()
{cin >> n;vector<int>v(n);info* root = nullptr;;for (int i = 0; i < n; i++){cin >> v[i];insert(root, v[i]);}dfs(root, 1);cout << num[minx] << " + " << num[minx - 1] << " = " << num[minx] + num[minx - 1];
}