What is a 'Radix Tree' (Patricia Trie)?

What is a 'Radix Tree' (Patricia Trie)?

Approach: Describe a space-optimized version of a Trie.

A space-optimized trie in which each node that is the only child is merged with its parent. It is highly efficient for storing strings with long common prefixes.

Follow-up: Where is this used (e.g., routing tables)?

Key concepts: compressed nodes, memory efficiency, prefix.