Summary

A doubly_linked_list is a sequence of nodes. Each node stores data plus prev and next links. It supports bidirectional_traversal. Common references are head and tail. Insert or remove at ends is efficient. Deleting a known node updates two links. Random access requires traversal. It is used in a deque and an lru_cache. Extra memory is needed for the second pointer. Typical pitfalls include broken links and orphan nodes.