題目：

思路：

程式碼：

struct TreeNode
{
	int val;
	TreeNode *left;
	TreeNode *right;
}

void Print(BinaryTreeNOde* pRoot)
{
	if(pRoot == NULL)
		return;
		
	stack<BinaryTreeNOde*>levels[2];
	int current = 0;
	int next = 1;
	
	levels[current].push(pRoot);
	while(!levels[0].empty() || !levels[0].empty())
	{
		BinaryTreeNOde* pNode = levels[current].top();
		levels[current].pop();
		
		printf("%d",pNode->val);
		
		if(current == 0)
		{
			if(pNode->left != NULL)
				levels[next].push(pNode->left);
			if(pNode->right != NULL)
				levels[next].push(pNode->right);
		}
		else
		{
			if(pNode->right != NULL)
				levels[next].push(pNode->right);
			if(pNode->left != NULL)
				levels[next].push(pNode->left);
		}
		
		if(levels[current].empty())
		{
			printf("\n");
			current = 1-current;
			next = 1-next;
		}
	}
}