DSA · Theory

If you are given two traversal sequences, can you construct the binary tree

Theory

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If you are given two traversal sequences, can you construct the binary tree

If you are given two traversal sequences, can you construct the binary tree is a DSA topic. In plain words you use it for folder on disk in a file explorer. Don’t start with a slogan — start with that picture.

Smallest example: left < root < right. Type it, run it, and say what you see. If you can do that from memory, you know If you are given two traversal sequences, can you construct the binary tree.

From the example next to this theory: If you are given two traversal sequences, can you construct the binary tree — inorder walks left → node → right (sorted order for a BST).

Trap — unbalanced BST becoming a list. Fix that before you talk about advanced DSA.

Viva: what is If you are given two traversal sequences, can you construct the binary tree? Then show left < root < right. Then name the trap.

Exam tip

What is If you are given two traversal sequences, can you construct the binary tree? Show this: left < root < right. Trap: unbalanced BST becoming a list.

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))

If you are given two traversal sequences, can you construct the binary tree — inorder walks left → node → right (sorted order for a BST).

Short notes

DefIf you are given two traversal sequences, can you construct the binary tree — folder on disk in a file explorer.
Ruleleft < root < right
Trapunbalanced BST becoming a list
Usea file explorer

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))

If you are given two traversal sequences, can you construct the binary tree

Example

Short notes

Questions

If you are given two traversal sequences, can you construct the binary tree

Example

Short notes

Questions