题目地址

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 [−10001000] 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>
#include <cmath>
#include<map>
#include<cstring>
#include<queue>
#include<string>
#include<set>
#include<stack>
using namespace std;
typedef long long ll;
const int maxn=10010,inf=100000000;
struct node{
    int data;
    node *lchild,*rchild;
};
int n,a[maxn];
void insert(node* &root,int data){
    if(!root){
        root=new node;
        root->lchild=root->rchild=NULL;
        root->data=data;
        return;
    }
    if(data<=root->data) insert(root->lchild,data);
    else insert(root->rchild,data);
}
int max_dep=0,next_dep=0,cnt_m,cnt_n;
void dfs(node *root,int dep){
    if(!root) return;
    if(dep>max_dep){
        max_dep=dep;cnt_m=1;
    }
    else if(dep==max_dep) cnt_m++;
    dfs(root->lchild,dep+1);
    dfs(root->rchild,dep+1);
}
void dfs2(node *root,int dep){
    if(!root) return;
    if(dep==max_dep-1)  cnt_n++;
    dfs2(root->lchild,dep+1);
    dfs2(root->rchild,dep+1);
}
int main(){
    cin>>n;
    node *root=NULL;
    for(int i=0;i<n;i++){
        cin>>a[i];
        insert(root,a[i]);
    }
    dfs(root,0);
    dfs2(root,0);
    printf("%d + %d = %d",cnt_m,cnt_n,cnt_m+cnt_n);
}