[C++知识库]PAT 1127. ZigZagging on a Tree (30)-甲级（简洁易懂）

#include<bits/stdc++.h>
using namespace std;
int  n,post[100001],in[100001],dd[100001],a,b,c,d;
struct node{
	node *lchild,*rchild;
	int deep;
	int data;
};
node *newnode(int yuy){
	node *Node=new node;
	Node->data=yuy;
	Node->lchild=NULL;
	Node->rchild=NULL;
	return Node;
}
void build(int inl,int inr,int postl,int postr,node* &root,int dep){
	if(postl>postr){
	root=NULL;
	return ;}
	int index;
	for(int i=inl;i<=inr;i++){
		if(post[postr]==in[i]){
			index=i;
			break;
		}
	}
	//printf("%d ",post[postr]);
	root=newnode(in[index]);
	root->deep=dep;
	dd[dep]++;
	build(inl,index-1,postl,postl+index-inl-1,root->lchild,dep+1);
	build(index+1,inr,postl+index-inl,postr-1,root->rchild,dep+1);
}

int main(){
	scanf("%d",&n);
	for(int i=1;i<=n;i++)scanf("%d",&in[i]);
	for(int i=1;i<=n;i++)scanf("%d",&post[i]);
	node *root=NULL;
	build(1,n,1,n,root,1);
//	dfs(root,1);
queue<node*>q;
q.push(root);
int ans[100001],kk=0;
while(!q.empty()){
	node *ui=q.front();
	q.pop();
	//printf("%d ",ui->data);
	ans[++kk]=ui->data;
//	if(ui->deep%2==1){
	if(ui->lchild)q.push(ui->lchild);
	if(ui->rchild)q.push(ui->rchild);
}
int ygg=1,u=1;
while(dd[ygg]){
	if(ygg%2==0)for(int i=u;i<=u+dd[ygg]-1;i++)printf("%d ",ans[i]);
	else for(int i=u+dd[ygg]-1;i>=u;i--)printf("%d ",ans[i]);
	u+=(dd[ygg]);
	++ygg;
}
	return 0;
}

Suppose that all the keys in a binary tree are distinct positive integers. A unique binary tree can be determined by a given pair of postorder and inorder traversal sequences. And it is a simple standard routine to print the numbers in level-order. However, if you think the problem is too simple, then you are too naive. This time you are supposed to print the numbers in "zigzagging order" -- that is, starting from the root, print the numbers level-by-level, alternating between left to right and right to left. For example, for the following tree you must output: 1 11 5 8 17 12 20 15.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤30), the total number of nodes in the binary tree. The second line gives the inorder sequence and the third line gives the postorder sequence. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print the zigzagging sequence of the tree in a line. All the numbers in a line must be separated by exactly one space, and there must be no extra space at the end of the line.