【PAT】1020. Tree Traversals (25)

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

---

分析：考察树的建立和遍历。

课参考《编程之美》3.9

 

#include<iostream>

#include<map>

#include<vector>

#include<queue>

using namespace std;



struct Node{

	Node *left;

	Node *right;

	int value;

	Node():left(NULL),right(NULL){}

};



void Rebuild(int * PostOrder, int * InOrder, int len, Node* &root){

	//判断何时结束递归

	if(PostOrder == NULL || InOrder == NULL)

	{

		root = NULL;

		return ;

	}

	if(root == NULL) root = new Node;

	root->value = *(PostOrder + len - 1);

	root->left = NULL;

	root->right = NULL;

	if(len == 1) 

		return;



	int count = 0;

	int *temp = InOrder;

	while(*temp != *(PostOrder + len -1))

	{

		count ++;

		temp++;

		if(count > len) break;

	}

	int left = temp - InOrder ;

	int right = len - left - 1;

	if(left > 0)

		Rebuild(PostOrder, InOrder, left, root->left);

	if(right > 0)

		Rebuild(PostOrder + left, InOrder+left+1, right, root->right);

}





int main()

{

	int n,i,t;

	while(cin>>n)

	{

		int *PostOrder = new int[n];

		int *InOrder = new int[n];

		for(i=0; i<n; i++)

			cin>>PostOrder[i];

		for(i=0; i<n; i++)

			cin>>InOrder[i];



		Node *root = new Node;

		int post_start,in_start;

		post_start = 0;

		in_start = 0;

		Rebuild(PostOrder, InOrder, n, root);

		queue<Node *> q;

		q.push(root);

		int flag = 1;



		while(!q.empty()){

			if(q.front()->left != NULL)

				q.push(q.front()->left);

			if(q.front()->right != NULL)

				q.push(q.front()->right);

			if(flag != n)

				cout<<q.front()->value<<" ";

			else 

				cout<<q.front()->value;

			flag ++;

			q.pop();

		}

		

		cout<<endl;

	}

	return 0;

}