Sudoku tips and strategies to solve harder puzzles
If you know the basic rules but get stuck on medium and hard puzzles, these techniques will help. They are listed from simplest to most advanced.
1. Scan rows, columns and boxes
Pick a number and check where it can still go in each box. Work through 1 to 9 in turn. Scanning finds most of the easy answers and is the fastest way to start.
2. Look at the fullest areas first
A row, column or box that already has seven or eight numbers is easy to finish. Complete those first, since each new number helps its neighbours.
3. Use pencil marks
List the possible numbers in each empty square. Keep them tidy and update them whenever you place a number. Good notes are what make hard puzzles possible.
4. Naked pairs
If two squares in the same row, column or box both contain only the same two possible numbers, such as 3 and 7, then those two numbers must go in those two squares. You can remove 3 and 7 from every other square in that row, column or box.
5. Hidden singles
Sometimes a number can go in only one square of a row, column or box, even though that square has other possibilities in its notes. Place the number there. To find them, look at one number at a time and ask where it can go in the unit.
6. Pointing pairs
If a number can only go in two or three squares of a box, and they all lie in one row, then that number must be in that row inside this box. You can remove it from the rest of the row outside the box. The same idea works for columns.
7. Box and line reduction
This is the reverse. If a number in a row can only go within one box, you can remove it from the other squares of that box.
Habits that help
- Play a puzzle every day. The daily puzzle on this site is the same for everyone.
- Move up one difficulty level only when the current one feels comfortable.
- Avoid hints until you have checked rows, columns and boxes for every number.
- Be consistent. Work through the grid in the same order each time.
Practice is the best teacher. Try each technique on a medium puzzle, then move on to hard.