types of traversals in a binary tree

There are three types of traversals in binary tree: pre-order, in-order and post-order

Lets take an example of BST

            20
    15              25
12      18      22      28

pre-order: visit each node before its children

public void preorder(BinaryNode root) {
  if(root !=  null) {
    System.out.println(root.element);
    preorder(root.left);
    preorder(root.right);
  }
}

Output: 20, 15, 12, 18, 25, 22, 28

in-order (applied only for binary trees): visit left sub-tree, node and then right sub-tree

public void inorder(BinaryNode root) {
  if(root !=  null) {
    inorder(root.left);
    System.out.println(root.element);
    inorder(root.right);
 }
} 

Output: 12, 15, 18, 20, 22, 25, 28
Note: If we notice the above elements they are all sorted which means the inorder traversal of any BST gives us the sorted elements.

post-order: visit each node after its children (left and right sub trees)

public void postorder(BinaryNode root) {
  if(root !=  null) {
    postorder(root.left);
    postorder(root.right);
    System.out.println(root.element);
 }
} 

Output: 12, 18, 15, 22, 28, 25, 20