1127. ZigZagging on a Tree (30)

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.

812 11 20 17 1 15 8 512 20 17 11 15 8 5 1Sample Output:
1 11 5 8 17 12 20 15
#include<cstdio>#include<vector>#include<queue>using namespace std;const int maxn = 35;int in[maxn], post[maxn];struct Node{	int data;	int depth;	Node*l, *r;	Node():l(NULL),r(NULL){}};int N, maxdepth = -1;Node*create(int i1, int i2, int p1, int p2){	if (i1 > i2 || p1 > p2)return NULL;	Node*root = new Node();	root->data = post[p2];	int k;	for (int i = i1; i <= i2; i++)	{		if (in[i] == root->data)		{			k = i; break;		}	}	root->l = create(i1, k - 1, p1, p1 + k - 1 - i1);	root->r = create(k+1, i2, p2-1-(i2-k-1), p2-1);	return root;}vector<int> nodes[maxn];void BFS(Node*root){	queue<Node*>Q;	root->depth = 0;	Q.push(root);	while (!Q.empty())	{		Node*f = Q.front();		Q.pop();		maxdepth = max(maxdepth, f->depth);		nodes[f->depth].push_back(f->data);		if (f->l)		{			f->l->depth = f->depth + 1;			Q.push(f->l);		}		if (f->r)		{			f->r->depth = f->depth + 1;			Q.push(f->r);		}	}}int main(){	scanf("%d", &N);	for (int i = 0; i < N; i++)		scanf("%d", &in[i]);	for (int i = 0; i < N; i++)		scanf("%d", &post[i]);	Node*root = NULL;	bool first = true;	root = create(0, N - 1, 0, N - 1);	BFS(root);	for (int i = 0; i <= maxdepth; i++)	{		if (i % 2 == 0)		{			for (int j = 0; j < nodes[i].size(); j++)			{				if (first)				{					first = false;					printf("%d", nodes[i][nodes[i].size() - 1 - j]);				}				else printf(" %d", nodes[i][nodes[i].size() - 1 - j]);			}		}		else		{			for (int j = 0; j < nodes[i].size(); j++)			{				if (first)				{					first = false;					printf("%d", nodes[i][j]);				}				else printf(" %d", nodes[i][j]);			}		}	}	return 0;}