PTA 7-3 lists leaf nodes

https://pintia.cn/problem-sets/1259041418971803648/problems/1259046259496415233
（ Title link above ）
Answer key ：
1, Store with structure array , Be careful char Convert to int.
2, utilize vis The array records the child nodes that have appeared , Then what does not appear is the root node .
3, Finally, sequence traversal （ Wide search ） Output leaf node .
AC Code ：

#include <iostream>
#include <queue>
using namespace std;
int leave[15],vis[30];
struct treenode{
    
	int num;
	int left,right;
}node[15];
int bfs(int rt){
    
	queue<treenode>q;
	q.push(node[rt]);
	int k=0;
	while(!q.empty()){
    
		treenode root=q.front();
		q.pop();
		int l,r;
		l=root.left; r=root.right;
		if(l==-1&&r==-1){
    
			leave[k++]=root.num;
		}
		if(l!=-1) q.push(node[l]);
		if(r!=-1) q.push(node[r]);
	}
	return k;
}
int main(){
    
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
    
		char l,r;
		cin>>l>>r;
		node[i].num=i;
		if(l=='-') node[i].left=-1;
		else{
    
			node[i].left=l-'0';
			vis[l-'0']=1;
		}
		if(r=='-') node[i].right=-1;
		else{
    
			node[i].right=r-'0';
			vis[r-'0']=1;
		}
	}
	int rt;
	for(int i=0;i<n;i++){
    
		if(!vis[i]){
    
			rt=i;break;
		}
	}
	int k;
	k=bfs(rt);
	for(int i=0;i<k;i++){
    
		if(i==0) cout<<leave[i];
		else cout<<" "<<leave[i];
	}
	cout<<endl;
	return 0;
}