Lowest Common Ancestor in Binary Tree | Dataford Interview Questions

Lowest Common Ancestor of a Binary Tree (LeetCode 236).

Asked in the Round 3 HM stage. Given a binary tree with unique integer values and two existing node values p and q, return the value of their lowest common ancestor. A node may be an ancestor of itself.

Input and Output

Implement lowest_common_ancestor(root, p, q). root is a nested dictionary with val, left, and right keys, where an absent child is null. Return the ancestor's integer value.

Constraints

1 <= number of nodes <= 10^5
Node values are unique integers
Both target values exist in the tree
The input is a binary tree, not necessarily a binary search tree

Function Signature

def lowest_common_ancestor(root, p, q):

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