将中序代码转换为前序和后序

Question

How do I turn this into a preorder and a postorder traversal? This code only traverses a tree in an inorder style.

void inorder() {
    inorderRec(root);
}

// Inorder Traversal
void inorderRec(Node root) {
    if (root != null) {
        inorderRec(root.left);
        System.out.print(root.key + " -> ");
        inorderRec(root.right);
    }
}

Answer 1

You can just change the order of statements:

void preOrderRec(Node root) {
    if (root != null) {
        System.out.print(root.key + " -> ");
        inorderRec(root.left);
        inorderRec(root.right);
     }

void postOrderRec(Node root) {
    if (root != null) {
        inorderRec(root.left);
        inorderRec(root.right);
        System.out.print(root.key + " -> ");
     }

Answer 2

void preOrder(Node root)
{
if (root) {
System.out.print(root.key + " -> ");
preOrder(root.left);
preOrder(root.right);
}
}

void postOrder(Node root)
{
if (root) 
{
postOrder(root.left);
postOrder(root.right);
System.out.print(root.key + " -> ");
}
}