DSA · Theory

Preorder Traversal

Theory

133/810

Preorder Traversal

Preorder Traversal is a DSA topic. In plain words you use it for a short Preorder Traversal example in a short dry-run on paper. Don’t start with a slogan — start with that picture.

Smallest example: the smallest Preorder Traversal example you can type. Type it, run it, and say what you see. If you can do that from memory, you know Preorder Traversal.

From the example next to this theory — Preorder Traversal — inorder walks left → node → right (sorted order for a BST).

Trap — only saying “Preorder Traversal” with no example. Fix that before you talk about advanced DSA.

Viva — what is Preorder Traversal? Then show the smallest Preorder Traversal example you can type. Then name the trap.

Exam tip

What is Preorder Traversal? Show this: the smallest Preorder Traversal example you can type. Trap: only saying “Preorder Traversal” with no example.

Example

class Node:
    def __init__(self, val, left=None, right=None):
        self.val, self.left, self.right = val, left, right

def inorder(n):
    if not n:
        return []
    return inorder(n.left) + [n.val] + inorder(n.right)

root = Node(2, Node(1), Node(3))
print(inorder(root))

Preorder Traversal — inorder walks left → node → right (sorted order for a BST).

Short notes

DefPreorder Traversal — a short Preorder Traversal example in a short dry-run on paper.
Rulethe smallest Preorder Traversal example you can type
Traponly saying “Preorder Traversal” with no example
Usea short dry-run on paper

DSA · Theory

Preorder Traversal

← All stacks

Theory

133/810

Preorder Traversal

Preorder Traversal is a DSA topic. In plain words you use it for a short Preorder Traversal example in a short dry-run on paper. Don’t start with a slogan — start with that picture.

Smallest example: the smallest Preorder Traversal example you can type. Type it, run it, and say what you see. If you can do that from memory, you know Preorder Traversal.

From the example next to this theory — Preorder Traversal — inorder walks left → node → right (sorted order for a BST).

Trap — only saying “Preorder Traversal” with no example. Fix that before you talk about advanced DSA.

Viva — what is Preorder Traversal? Then show the smallest Preorder Traversal example you can type. Then name the trap.

Exam tip

What is Preorder Traversal? Show this: the smallest Preorder Traversal example you can type. Trap: only saying “Preorder Traversal” with no example.

Example

class Node:
    def __init__(self, val, left=None, right=None):
        self.val, self.left, self.right = val, left, right

def inorder(n):
    if not n:
        return []
    return inorder(n.left) + [n.val] + inorder(n.right)

root = Node(2, Node(1), Node(3))
print(inorder(root))

Preorder Traversal — inorder walks left → node → right (sorted order for a BST).

Short notes

DefPreorder Traversal — a short Preorder Traversal example in a short dry-run on paper.
Rulethe smallest Preorder Traversal example you can type
Traponly saying “Preorder Traversal” with no example
Usea short dry-run on paper

Preorder Traversal

Example

Short notes

Questions

Preorder Traversal

Example

Short notes

Questions