用伪代码编写先序遍历中序遍历后序遍历

1. 先序遍历

preorder(node)
    if node is not null
        print node.value
        preorder(node.left)
        preorder(node.right)

2. 中序遍历

inorder(node)
    if node is not null
        inorder(node.left)
        print node.value
        inorder(node.right)

3. 后序遍历

postorder(node)
    if node is not null
        postorder(node.left)
        postorder(node.right)
        print node.value