PUZZLE TECHNIQUES

SANDWICH SUDOKU TECHNIQUES

Learn advanced techniques to solve Sandwich Sudoku puzzles. When you know all our tips, then it will be easier to play sandwich sudoku online.

We have created a step by step discussion on how to solve a Sandwich Sudoku and learn all the techniques.

Like always: only use logic to find the solution.

LIST WITH COMBINATIONS

When solving a Sandwich Sudoku you see the sum of the digits between 1 and 9 outside the frame. It is helpful to know how many cells each sum needs. For eg. numbers 2, 3 and 4 ALWAYS need 1 cell and numbers 31, 32 and 33 ALWAYS need 6 cells.

Therefore we have created a list with all the sum combinations. Look HERE for a overview of all the combinations with the numbers 5 - 35.

LOOK FOR SUM 35

If you have the number 35 as a clue, then that is an easy start because 35 needs 7 cells. So 1 and 9 must be in the first and last cell.

In cell R8C9 we already have "9" so we can place "1" in R2C9 and "9" in R2C1.

TRY TO FIND 19-COMBINATIONS

Use the information outside the grid and the digits on the grid to find as many 19-combinations as possible. We try to achieve this through identifying the cells in the sandwich sudokus that cannot contain "1" or "9" and color them "yellow" by clicking on them. At the start of this sudoku we have "1" in the middle and "1" at the right top

LOOK FOR SUM 31, 32 OR 33

What do we know about those numbers? Those numbers have only 1 combination and always need 6 cells. So the digit that doesn't belong to the combination is in the first or last cell. The "?" is the place of 1 or 9

• 31 will give ?235678?4 or 4?235678?.
• 32 will give ?255678?3 or 3?245678?.
• 33 will give ?345678?2 or 2?345678?.

We color the cell that can't have a 1 or 9 in row 2.

ENOUGH SPACE

if we have large numbers in the frame of a sandwich sudoku, then we need enough space. This means enough cells to place the digits.

When we look at row 5 in the example below, then we can place "9" in column 4 or column 6. But column 4 tells us we need to have "23" between 1 and 9 and in our list we see that "23" takes 4 or 5 cells to create.

So there is not enough space to create "23" if we place the "9" in R5C4. Consequently the "9" only fits in R5C6.

SUM > 21 OR SUM > 26

The higher the numbers in the frame, the more squares they need.

• Sum numbers in the frame that are 22 or more: you can exclude the middle cell as a place for 1 or 9.
• Sum numbers in the frame that are 27 or more: you can exclude the three middle cells as places for 1 or 9

EXCLUDING TECHNIQUE

We find the "1" in R7C2 using the enoogh space technique. We need 3 or 4 cells for 16. There is already a "1" in column 3. So we need a 4-cell combination for 16.

Now we try to find the combination in column 2. It can be 941 or 149. It can't be 149 because we need a 19 or 91 combination in row 9 and we can't have two 9's in one box.

SUM OUTSIDE 1 & 9

When we have eg. 25 in column 9, then we know that we will have a total of 10 outside the 19-group. We have "2" in R2C9, so the outside group will be 8 split into 2 cells with 3 or 5.

1 COMBINATION TECHNIQUE

Sometimes sandwich sudokus havee SUMNUMBERS with only 1 combination. If we look at column 5 below, then we need to divide 15 into 4 cells. There is only one possibility with the numbers 2346. So we also know that we can place 578 in column 5 of box 8. As a result, we also know that 346 belongs in column 4 of box 8.