How to use the bank: don't grind top-to-bottom. Pick the topic you just finished in Phases 2–4, clear its Easies to warm up, then live in the Mediums — they're what interviews are made of. Only open the hint after 15 minutes of honest effort; the cue names the pattern, and the pattern cheatsheet has the full template. The C++ solution below each hint is a reference implementation — read it only after you have your own working version, and compare approaches. Re-solve anything you needed the hint for a week later.