1. Create binary search tree from sorted array or linked list: It cannot access element via index in linked list as array, it uses direction to next node. Array creates root by middle term first, but linked list creates left subtree.
2. Multiple solutions for a problem help build connection with knowledge graph. (Linked list reverse and rotate can transfer to each other)
3. Stack and Recursion are both reverse way to process data.
4. Stack can work as parent pointer for tree problem.
5. MongoDB: nested structure, no schema, horizontal scaling (replica, shard), application driven, not engineering driven
6. Pivot/MVP: change strategy without changing vision