PAT A 1020 Tree Traversals (25分)——给中序和后序求层序

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本文探讨了如何从给定的二叉树中序和后序遍历序列中，构建对应的二叉树，并输出该树的层序遍历序列。通过递归方式创建二叉树节点，再使用队列实现层序遍历，最后输出遍历结果。

1020 Tree Traversals (25分)
Suppose that all the keys in a binary tree are distinct positive integers. Given the postorder and inorder traversal sequences, you are supposed to output the level order traversal sequence of the corresponding binary tree.

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 postorder sequence and the third line gives the inorder sequence. All the numbers in a line are separated by a space.

Output Specification:
For each test case, print in one line the level order traversal sequence of the corresponding binary tree. 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.

Sample Input:
7
2 3 1 5 7 6 4
1 2 3 4 5 6 7
Sample Output:
4 1 6 3 5 7 2
思路：
给中序和后序求层序
在这里插入图片描述
代码：

#include<bits/stdc++.h>
using namespace std;
const int maxn=50;
struct node{
	int data;
    node* lchild;
	node* rchild;
};
int in[maxn],post[maxn];
int n;
node* creat(int postL,int postR,int inL,int inR){
	if(postL>postR){
		return NULL;
	}
      node* root = new node;
      root->data=post[postR];
      int k;
      for(k=1;k<=inR;k++){
      	if(post[postR]==in[k])break;
	  }
	  int numleft = k-inL;
	  root->lchild=creat(postL,postL+numleft-1,inL,k-1);
	  root->rchild=creat(postL+numleft,postR-1,k+1,inR);
	  return root;
}
int num=0;
void BFS(node* root){
	queue<node*> q;
	q.push(root);
	while(!q.empty()){
		node* now = q.front();
		q.pop();
		printf("%d",now->data);
		num++;
		if(num<n)printf(" ");
		if(now->lchild != NULL) q.push(now->lchild);
		if(now->rchild != NULL) q.push(now->rchild);
	}
	
}
int main(){

	scanf("%d",&n);
    for(int i=1;i<=n;i++) scanf("%d",&post[i]);
    for(int i=1;i<=n;i++) scanf("%d",&in[i]);
    node* root=creat(1,n,1,n);
    BFS(root);
    return 0;
}