第四十三题（递归和非递归俩种方法实现二叉树的前序遍历）

namespace MS100P_43
{
	struct TreeNode
	{
		int data;
		TreeNode *left;
		TreeNode *right;
	};
	void preOrderTranverse_recursive(TreeNode* root)
	{
		if (root == NULL)	return;
		cout << root->data << ' ';
		preOrderTranverse_recursive(root->left);
		preOrderTranverse_recursive(root->right);
	}
	void preOrderTranverse_nonRecursive(TreeNode* root)
	{
		if (root == NULL)	return;
		stack<TreeNode*> s;
		while (root != NULL || !s.empty())
		{
			while (root != NULL)
			{
				cout << root->data << ' ';
				s.push(root);
				root = root->left;
			}
			if (!s.empty())
			{
				root = s.top();
				root = root->right;
				s.pop();
			}
		}
	}

}