Pat grade a a1086 tree traversals again

The question ： Stack in and out （push,pop） To determine the unique binary tree , One of the sequences is known to be middle order traversal , To find the subsequent traversal .

analysis ：
From the meaning of the question , In a certain order of entering and leaving the stack , Two sequences can be determined , therefore , It should be that the stack entry is a traversal sequence , Stack is also a traversal sequence , Because the title gives ,"An inorder binary tree traversal", therefore , There is a sequence that should be a middle order traversal sequence , And preorder traversal is to visit the root node first , And the nature of the stack sequence process , You can first think of the stack order as a sequence of preorder traversal , Thus, the unique binary tree can be determined , By outputting samples, it can be found that the post order traversal sequence is consistent with the post order traversal sequence of the binary tree , Therefore, it can be concluded that the stacking order is the preorder traversal sequence , Out of the stack is a middle order traversal sequence  

The tree is shown in the figure ：

Ideas ： Set of templates ;

Code ：

#include<iostream>
#include<stack>
using namespace std;
const int maxn=50;
int n;
int in[maxn],pre[maxn];
int preindex=0,inindex=0;
struct node{
	int data;
	node* lchild;
	node* rchild;
};
node* create(int preL,int preR,int inL,int inR){
	if(preL>preR)return NULL;
	node* root=new node;
	root->data=pre[preL];
	int k=inL;
	for(k=inL;k<=inR;k++){
		if(in[k]==root->data)break;
	}
	int leftnum=k-inL;
	root->lchild=create(preL+1,preL+leftnum,inL,k-1);
	root->rchild=create(preL+leftnum+1,preR,k+1,inR);
	return root;
}
int m=0;
void postorder(node* root){// After the sequence traversal -- Left and right ; 
	if(root==NULL)return ;
	postorder(root->lchild);
	postorder(root->rchild);
	printf("%d",root->data);
	m++;
	if(m<n)printf(" ");
}
int main( ){
	scanf("%d",&n);// Number of nodes ; 
	getchar( );
	stack<int > s;
	string str;
	int num;
	for(int i=0;i<2*n;i++){// Out of the stack , So it is 2n 
		cin>>str;// Out-of-service scanf Input string type , If you use printf Output string Type to use .c_string transformation ; 
		if(str=="Push"){
			scanf("%d",&num);			
			s.push(num);
			pre[preindex++]=num;
		}else {
			in[inindex++]=s.top();// The stack takes out the top element with top; 
			s.pop( );
		}
	}
	node* root=create(0,n-1,0,n-1);
	postorder(root);
	return 0;
}

Be careful ： Do not use scanf Input string type , Want to use printf Output string Type to use str.c_str() function .