DSA · Theory

Lowest Common Ancestor of a Binary Tree

Theory

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Lowest Common Ancestor of a Binary Tree

Lowest Common Ancestor of a 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 Lowest Common Ancestor of a Binary Tree.

From the example next to this theory: Lowest Common Ancestor of a 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 Lowest Common Ancestor of a Binary Tree? Then show left < root < right. Then name the trap.

Exam tip

What is Lowest Common Ancestor of a 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))

Lowest Common Ancestor of a Binary Tree — inorder walks left → node → right (sorted order for a BST).

Short notes

DefLowest Common Ancestor of a 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))

Lowest Common Ancestor of a Binary Tree

Example

Short notes

Questions

Lowest Common Ancestor of a Binary Tree

Example

Short notes

Questions