1. Solving Sudoku Mark PTTLS Micro teach

2. Solving Sudoku What is a Sudoku? A Sudoku is a number puzzle based on a 9x9 grid made up from smaller 3x3 blocks. The numbers 1 to 9 have to be entered into the grid to solve the puzzle. You are given a certain amount of numbers to start you off.

3. Solving Sudoku What are the rules? There is one main rule in Sudoku: The numbers 1 to 9 are to be entered into the grid so that each number appears only once in each Row, Column and Block. Each Sudoku has a unique solution.

4. Solving Sudoku Where did Sudoku come from? Sudoku was first invented in America in 1979 by Howard Garns who called them “Number Place”. The puzzles were introduced into Japan in 1984 by the Nikoli publishing company who called them “Suuji wa dokushin ni kagiru” (the digits must be single), which was shortened to "Sudoku". They were then introduced into the UK in 2004 by The Times who called them “Su Doku”.

5. Solving Sudoku What was that rule again? You start with a grid with some numbers in it…

6. Solving Sudoku What was that rule again? You start with a grid with some numbers in it… …and you fill in the missing numbers.

7. Solving Sudoku What was that rule again? The numbers 1-9 appear just once in each: Row

8. Solving Sudoku What was that rule again? The numbers 1-9 appear just once in each: Row Column

9. Solving Sudoku What was that rule again? The numbers 1-9 appear just once in each: Row Column Block

10. Solving Sudoku What was that rule again? The numbers 1-9 appear just once in each: Row Column Block Note: Each number can only appear ONCE in its own Row, Column and Block… This area is known as its scope.

11. Solving Sudoku Solution method: Cross hatching Cross hatching uses the numbers already on the grid. These numbers point to new numbers. It is easy and it is fast.

12. Solving Sudoku Solution method: Cross hatching Consider the 1’s

13. Solving Sudoku Solution method: Cross hatching Consider the 1’s Consider the centre Block.

14. Solving Sudoku Solution method: Cross hatching Consider the 1’s Consider the centre Block. The 1’s here claim the two lower rows.

15. Solving Sudoku Solution method: Cross hatching Consider the 1’s Consider the centre Block. The 1’s here claim the two lower rows. There is only one place for a 1 in this Block.

16. Solving Sudoku Solution method: Cross hatching Consider the 1’s Consider the centre Block. The 1’s here claim the two lower rows. There is only one place for a 1 in this Block. The 1 is written in.

17. Solving Sudoku Solution method: Cross hatching Now consider the top left Block.

18. Solving Sudoku Solution method: Cross hatching Now consider the top left Block. The two 1’s here claim these cells.

19. Solving Sudoku Solution method: Cross hatching Now consider the top left Block. The two 1’s here claim these cells. There is only one place for a 1 in this Block.

20. Solving Sudoku Solution method: Cross hatching Now consider the top left Block. The two 1’s here claim these cells. There is only one place for a 1 in this Block. The 1 is written in.

21. Solving Sudoku Solution method: Cross hatching Consider the 2’s

22. Solving Sudoku Solution method: Cross hatching Consider the 2’s Consider the top left Block.

23. Solving Sudoku Solution method: Cross hatching Consider the 2’s Consider the top left Block. The 2’s here claim the top two rows.

24. Solving Sudoku Solution method: Cross hatching Consider the 2’s Consider the top left Block. The 2’s here claim the top two rows. There is only one place left for a 2 in this Block.

25. Solving Sudoku Solution method: Cross hatching Consider the 2’s Consider the top left Block. The 2’s here claim the top two rows. There is only one place left for a 2 in this Block. The 2 is written in.

26. Solving Sudoku Solution method: Cross hatching Consider the 3’s

27. Solving Sudoku Solution method: Cross hatching Consider the 3’s Consider the top left Block.

28. Solving Sudoku Solution method: Cross hatching Consider the 3’s Consider the top left Block. The 3’s here claim their two columns.

29. Solving Sudoku Solution method: Cross hatching Consider the 3’s Consider the top left Block. The 3’s here claim their two columns. There is only one place left for a 3 in this Block.

30. Solving Sudoku Solution method: Cross hatching Consider the 3’s Consider the top left Block. The 3’s here claim their two columns. There is only one place left for a 3 in this Block. The 3 is written in.

31. Solving Sudoku Activity: Try out this sample Sudoku: Use cross hatching to search for hidden singles. Try each number in turn. If you don’t find anything try the next number. Do not guess!

32. Solving Sudoku Solution method: Counting A second method to try is counting off all the numbers in a Row, Column or Block. Always fill in the last number left in a House. Counting can also reveal numbers that cross hatching can’t.

33. Solving Sudoku Solution method: Counting Consider the middle Block. All the numbers are there apart from 2, 6 and 9.

34. Solving Sudoku Solution method: Counting Now consider the highlighted cell in middle Block.

35. Solving Sudoku Solution method: Counting Now consider the highlighted cell in middle Block. Counting the scope of the cell reveals all the numbers are present apart from 6.

36. Solving Sudoku Solution method: Counting Now consider the highlighted cell in middle Block. Counting the scope of the cell reveals all the numbers are present apart from 6. 6 can be written in. (Counting can be hard to spot).

37. Solving Sudoku Solution method: Cross hatch with pointing Sometimes a number can be found even though not all the information is there. Empty cells may be claiming a number and be pointing to other cells.

38. Solving Sudoku Solution method: Cross hatch with pointing Consider the 5’s

39. Solving Sudoku Solution method: Cross hatch with pointing Consider the 5’s Consider the bottom right Block.

40. Solving Sudoku Solution method: Cross hatch with pointing Consider the 5’s Consider the bottom right Block. The 5’s here claim cells - but there is not enough information. A number cannot be written in.

41. Solving Sudoku Solution method: Cross hatch with pointing Now look at the top left block. One of the highlighted cells must be a 5.

42. Solving Sudoku Solution method: Cross hatch with pointing Now look at the top left block. One of the highlighted cells must be a 5. So that column is claimed.

43. Solution method: Cross hatch with pointing Solving Sudoku Now look at the top left block. One of the highlighted cells must be a 5. So that column is claimed. …now a cell is found.

44. Solution method: Cross hatch with pointing Solving Sudoku Now look at the top left block. One of the highlighted cells must be a 5. So that column is claimed. …now a cell is found. And 5 can be written in.

45. Solving Sudoku Activity: Try out this sample Sudoku: Use cross hatching to search for hidden singles. Try each number in turn. If you don’t find anything try the next number. Do not guess!

46. Solving Sudoku Recap: A Sudoku is a number puzzle based on a 9x9 grid made up from smaller 3x3 blocks. The numbers 1 to 9 have to be entered into the grid to solve the puzzle. Each Row, Column, Block must use the 1-9 numbers once (Sudoku). Cross Hatching and Counting are two solution methods.

47. Solving Sudoku Activity: SOLUTION Use cross hatching to search for hidden singles. Try each number in turn. If you don’t find anything try the next number. Do not guess!