DS binary tree - parent and child nodes of binary tree

Title Description

The logical structure of a given binary tree is shown in the figure below ,（ The result of preorder traversal , Empty tree character ‘0’ Express , for example AB0C00D00）, The binary chain storage structure of the binary tree is established .

Write a program to output all leaf nodes and their parent nodes of the tree

Input

Enter an integer in the first line t, Express t A binary tree

From the second line , According to the input method represented by the title , Enter the pre order traversal of each binary tree , Continuous input t That's ok

Output

The first line is traversed in order , Output No 1 Leaf node of an example

The second line outputs 1 In the first example, the parent node corresponding to the leaf

And so on, output the results of other examples

   The sample input

3
AB0C00D00
AB00C00
ABCD0000EF000

Sample output

C D 
B A 
B C 
A A 
D F 
C E 

Code

#include<bits/stdc++.h>
using namespace std;
int t;
string s,ans;
struct NODE{
	char data;
	NODE *l,*r;
	NODE (){
		l=NULL;
		r=NULL;
	}
};

int id=0,n;
void build(NODE *&head){
	if(id>=n || s[id]=='0'){
		head=NULL;
		id++;
		return ;
	}
	head=new NODE;
	head->data=s[id];
	id++;
	build(head->l);
	build(head->r);
}

void dfs(NODE *node,NODE *fa){
	if(node->l==NULL && node->r==NULL){
		cout<<node->data<<" ";
		ans=ans+fa->data+" ";
		return ;
	}
	if(node->l){
		dfs(node->l,node);
	}
	if(node->r){
		dfs(node->r,node);
	}
}

int main(){
	cin>>t;
	while(t--){
		cin>>s;
		n=s.length();
		NODE *head=new NODE;
		id=0;
		ans="";
		build(head);
		dfs(head,head);
		cout<<endl<<ans<<endl;
	}
	return 0;
}