非递归方式先序+中序+后序遍历二叉树

void preOrder(BTNode * head) {
		if (head == null)  return ;
		Stack<Node> stack = new Stack<BTNode *>();
		stack.push(head);
		while (!stack.isEmpty()){			
			head= stack.top(); 
			cout<<head->data<<" ";
			stack.pop();
			if(head.right != null) stack.push(head.right);
			if(head.left != null) stack.push(head.left);
		}
}


void inOrder(BTNode * head) {
	if (head == null)  return ;
	Stack<Node> stack = new Stack<Node>();
	while (!stack.isEmpty() || head != null){
		if (head != null){
			stack.push(head);
			head = head.left;
		} else{
			head = stack.pop();
			cout<<head->data<<" ";
			head = head.right;
		}
	}
}

void postOrder(BTNode * head){
	if (head == null) return ; 
		Stack<Node> s1 = new Stack<Node>();
		Stack<Node> s2 = new Stack<Node>();
		s1.push(head);
		while (!s1.isEmpty()){
			head = s1.pop();
			s2.push(head);
			if(head.left != null) s1.push(head.left);
			if (head.right != null) s1.push(head.right);
		}
		while (!s2.isEmpty()){
			BTNode * cur=s2.pop();
			cout<<cur->data<<" ";
		}
}