PAT-A-1020-Tree Traversals

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

Code

#include <iostream>
#include <queue>
using namespace std;
struct node {
	int data;
	node* lc, * rc;
	node(int data) :data(data), lc(0), rc(0) {}
};

int postseq[30], inseq[30];

//用后序遍历和中序遍历构建树，并返回根节点
node* buildTree(int postL, int postR, int inL, int inR) {
	if (postL > postR)
		return 0;
	node* root = new node(postseq[postR]);
	int i;
	for (i = inL;i <= inR;i++) {
		if (root->data == inseq[i])
			break;
	}
	//左子树的节点个数
	int lnums = i - inL;
	root->lc = buildTree(postL, postL + lnums - 1, inL, i - 1);
	root->rc = buildTree(postL + lnums, postR - 1, i + 1, inR);
	return root;
}

void levelOrder(node* root) {
	queue<node*> q;
	q.push(root);
	node* temp;
	int cnt = 0;
	while (!q.empty()) {
		temp = q.front();
		q.pop();
		if (cnt++ == 0)
			printf("%d", temp->data);
		else
			printf(" %d", temp->data);
		if (temp->lc!=0) {
			q.push(temp->lc);
		}
		if (temp->rc != 0) {
			q.push(temp->rc);
		}
		
	}
}

int main() {
	int n, i, j;//节点的个数
	scanf("%d", &n);
	for (i = 0;i < n;i++)
		scanf("%d", &postseq[i]);

	for (j = 0;j < n;j++)
		scanf("%d", &inseq[j]);

	node* root = buildTree(0, n - 1, 0, n - 1);
	levelOrder(root);

	return 0;
}