Stage 0 Review Pack 01¶

This pack is for retrieval after first exposure, not for learning these ideas for the very first time.

Who This Is For¶

Use this pack if you have already read most of the beginner route and want one short session that mixes the first useful ideas:

Try this pack only if these already feel familiar enough that you can begin without opening the note immediately:

Slot	Problem	Topic	Why it is here
1	Missing Number	`C++ language`	Clean start, zero friction, gets you compiling and settling in.
2	Ferris Wheel	`Sorting / greedy pairing`	Quick retrieval of sorted scans and pairing logic.
3	Static Range Sum Queries	`Prefix sums`	Checks whether you can still derive range answers from one invariant.
4	Apartments	`Two pointers`	Forces you to justify pointer movement rather than cargo-culting it.
5	Message Route	`Graph modeling + BFS`	Ends the pack with a genuine graph state switch and path reconstruction.

do not open the stored notes first
solve each problem in order with one honest attempt
after each accepted solution, compare your invariant with the repo note
if a problem stalls for longer than about 15 minutes, open at most one refresher page, not the solved note
if you still cannot restart after about 25 minutes, log the missing recognition cue and move on

After the pack, write down:

Which problem you recognized immediately and why.
Which invariant you kept forgetting.
Whether your first graph instinct is now “model the vertices and edges first” instead of “which algorithm do I know?”