Tree deletion, rollback, and route checks

Check the structure that remains after deletion, the history retained for rollback, and the heap entry that still represents the best route.

Lessons

• Red-black deletion: move color before removing a key
• AVL interval deletion: repair balance and maximum endpoints
• Disjoint-set rollback: restore an earlier connectivity checkpoint
• Shortest routes: skip stale min-heap entries

Design exercise

• Project: test depot rollback, routes, and ordered deletion
• Data Structures