Expert is the hardest level here. With so few givens, fill in candidates first and work through them with patterns. Every puzzle has exactly one solution.
Expert strategy
- Start by pencilling candidates into every empty cell. At Expert, your notes are the map.
- Hidden pair: when two numbers can only go in the same two cells of a unit, remove every other candidate from those cells.
- X-Wing: if a number's candidates in two rows sit in the same two columns, remove it from those columns in the other rows.
- Stuck? Look again around the last number you placed. One placement often unlocks the next.