Sudoku

Medium puzzles introduce a technique that easy puzzles skip entirely: hidden singles. A hidden single is a number that can only go in one cell within a row, column, or box — even though that cell might have multiple candidates. You won't always spot them through scanning alone, which is exactly what makes medium the first real step up.

This is where pencil marks start earning their keep. You don't need to annotate every cell — just the ones where scanning leaves you stuck. Write down the possibilities, then look unit by unit. If a particular number shows up as a candidate in only one cell within a row, column, or box, that cell is solved. The number might be hiding among three or four other candidates, but it has nowhere else to go.

Medium puzzles typically have 28 to 34 clues. Fewer givens means more ambiguity in the early stages, but the solving path stays purely logical from start to finish. If you ever find yourself wanting to guess, stop. Re-scan the grid from scratch. There's always a deduction you haven't found yet — the puzzle wouldn't be here otherwise.

The gap between medium and hard is the biggest jump in the game. Medium asks you to find hidden singles; hard asks you to find pairs and triples. Once medium feels comfortable — say, finishing consistently in 8 to 12 minutes — give hard a shot. The techniques are different, but you'll have the scanning instincts and pencil mark habits to handle it.