| Book | Focus | Difficulty | Solutions | |------|-------|------------|-----------| | | Selected topics + problem solving | Medium–Hard (olympiad training) | Full, detailed | | Problem-Solving Strategies (Engel) | Broad strategies (pigeonhole, invariants, etc.) | Hard (IMO level) | Mostly sketches | | The USSR Olympiad Problem Book (Shklarsky et al.) | Classic Soviet olympiad problems | Hard | Full solutions | | How to Solve It (Polya) | Heuristics, not problem sets | Easy–Medium | No solutions |
Dorofeev’s book occupies a sweet spot: more systematic than Shklarsky, more accessible than Engel, and more problem-focused than Polya. | Book | Focus | Difficulty | Solutions