1115 counting nodes in a BST (30 points)

The main idea of the topic ： According to the given sequence , Build a binary search tree , Find the number of nodes in the last two layers

Insert node tree , Search wide or deep to find the number of nodes in each layer

#include <iostream>
#include <queue>
#include <unordered_map>
using namespace std;
int n,x,f;
unordered_map<int,int>mp;
struct node
{
	int v;
	node *left,*right;
	node(int x): v(x),left(NULL),right(NULL){}
}*tr;
node *insert(node *t,int val)
{
	if(t == NULL) t = new node(val);
	else if(t -> v < val) t -> right = insert(t -> right,val);
	else t -> left = insert(t -> left,val);
	return t;
}
void bfs(node *tr)
{
	queue<pair<node*,int>>que;
	que.push({tr,0});
	while(que.size())
	{
		auto t = que.front();que.pop();
		auto u = t.first;f = t.second;
		mp[f] ++;
		if(u -> left != NULL) que.push({u -> left,f + 1});
		if(u -> right != NULL) que.push({u -> right,f + 1});
	}
}
int main()
{
	cin >> n;
	for(int i = 0; i < n; i ++)
	{
		cin >> x;
		tr = insert(tr,x);
	}
	bfs(tr);
	int d1 = mp[f],d2 = mp[f - 1];
	printf("%d + %d = %d",d1,d2,d1 + d2);
	return 0;
}