DSA · Theory

Preorder Traversal

Theory

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Preorder Traversal

If you can teach Preorder Traversal using Preorder Traversal on Amit's board, you know it. If you only know the heading, you don’t.

Preorder Traversal on the board: one Preorder Traversal step Amit can write from memory. Then say what Preorder Traversal on Amit's board looks like after.

Without Preorder Traversal, a viva board gets messy and Preorder Traversal on Amit's board is hard to trust.

Preorder Traversal shows up in a viva board. Name Preorder Traversal on Amit's board, not “a real-world scenario”.

If Preorder Traversal on Amit's board breaks under Preorder Traversal, check skipping the failure case for Preorder Traversal first.

After Preorder Traversal, Amit should still remember skipping the failure case for Preorder Traversal.

Viva for Preorder Traversal: what it is → one Preorder Traversal step Amit can write from memory → the mistake (skipping the failure case for Preorder Traversal).

Exam tip

For Preorder Traversal: definition + a viva board + one failure.

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 — Amit uses it for Preorder Traversal on Amit's board in a viva board.
RulePreorder Traversal → one Preorder Traversal step Amit can write from memory.
RememberPreorder Traversal + time vs memory (a viva board).
UsePreorder Traversal in a viva board (Preorder Traversal on Amit's board).
TrapPreorder Traversal — skipping the failure case for Preorder Traversal.
ExPreorder Traversal → Preorder Traversal on Amit's board.

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

Example

Short notes

Questions

Preorder Traversal

Example

Short notes

Questions