## Sandwich Sudoku Online Help

### Introduction

Sandwich Sudoku follows the same rules as regular Sudoku in that each row, column and block must contain one of the numbers from "1" to "9". No number may appear more than once in any row, column, or block.
It differs in that it displays a number for each row and column. This number is the total of the cell contents that are between the "1" and the "9" for the corresponding row/column.

For example, in the puzzle to the right, in row 3 the sum of digits between the "1" and "9" must be 4. There is only one combination that gives 4 (ie the digit 4 itself) so the cell to the right of the "1" must be a "4" and the cyan colored cell must be a "9". Similarly, in row 5 the total must be 32. The only possibility for that is a combination of the digits "245678" ie 6 cells. So the "9" can only be in the cyan colored cell and the cell in column 1 has to be a "3".
It is recommended that you watch the video walkthrough to get tips on solving strategies.

### How To Play

• There is one new puzzle per day which is automatically loaded when you open the page.
• Fill in blanks with the Pen (select a cell, then click on the number you want to enter).
• If you're not 100% sure of a number, you can make a note of it in the cell using the Pencil. To do this, click the "Pencil" icon to be placed in "Pencil mode".
• You may enter as many pencil marks as you like in each cell.
• To change back to "Pen" mode, click the "Pen" icon. You can also switch between pen and pencil modes quickly by pressing the "P" key or by using the mouse wheel. (See tips below.)

### Input Tips

#### Keyboard

If you prefer to use the keyboard rather than the mouse, you may:
• Use the arrow keys to navigate around the grid.
• Use the number keys to enter a number in the highlighted cell.
• Press the space or Delete key to remove any numbers from the highlighted cell.
• Press the "P" key to toggle between Pen and Pencil or use the mouse wheel.
• Press the "U" key to undo last input.
• Press the "C" key to change all cells with one possible (pencil mark) to pen.
• Hold Shift key down to always enter in pencil (not operable with the number pad).

#### Other Tips

• Clicking the Sandwich total numbers at the end of each row or below each column will show all the possible digit combinations that sum to that number. Of course the digits may be in any order in the sandwich cells (ie those cells between the "1" and "9").
• For every row or column, the sum of the digits (1-9) equals 45. So all the non-sandwich cells for a row or column will equal (45 - sandwich total - 10) (the 10 is the sum of "1" and "9"). That is, all cells outside of the "1" and "9" will total (35 - sandwich total). If for example there are 3 non-sandwich cells and you wish to know the digit combinations that make that total, you can use the button to see combinations for any total and number of cells.
• Click the Undo icon (yellow arrow) to undo last input. You can undo all the way back to the beginning.
• Holding the Shift key when clicking on a number in the input panel will pencil that number in. You may find this more convenient than toggling between the Pen and Pencil icons.
• To remove just one pencilled number in a cell, enter that number again.
• To remove all pencil numbers in a cell, either click the eraser button or simply "pen" the final choice in.
• To remove all pencil marks from all cells, use the menu option under "Edit".
• There is an alternate mode of number input via the mouse called "Active Number Mode" (see below).

### Active Number Mode

If you select this mode (via Edit->Preferences menu option), then the number you click from the Number Pad on the right becomes the "active number". The mouse cursor will change to this number and clicking on any cell will enter it in that cell. This is the reverse of the "cell select" mode, where you highlight a cell and then select the number to input. Those that prefer to solve by focusing on one specific number at a time will find this mode much more convenient.

To change the active number, select a new one from the Number Pad or scroll the mouse wheel down/up to increase/decrease the number. (If not in Active Number Mode, the mouse wheel will toggle between pen and pencil.)

In the Active Number mode, all pencil functionality remains the same as does the ability to use the keyboard.

### Description Of Menu Options

#### Edit Menu

##### Undo
Undoes the last input. You can undo right back to the beginning of the puzzle (unless you loaded a partially solved one). There is an Undo button which performs the same task, also the "U" key is a shortcut to this option.
##### Clear Possibles
This will clear all possibles displayed in the grid.
##### Clear All Input
This will clear all input (pen and pencil marks) displayed in the grid.
##### Pencil Marks to Pen
This option will convert all cells that have one pencil mark to a pen mark. The "C" key is a shortcut key for this option.
##### Save
Saves the current state of the puzzle to temporary user data on this computer. This is useful if you wish to come back another time to continue solving it, or if you are guessing which may necessitate you to backtrack later on.
##### Load
Loads the last saved puzzle on this computer.
##### Print
This will print the puzzle at the state it is currenly displayed in the grid.

#### Preferences

Here you may set various preferences. They are remembered and will reload from what was last set on that computer.

Active Number Mode: This toggle Active Number Mode, described above.

Show Pen/Pencil Cursor: Toggles whether the pen/pencil cursor is displayed over the grid or just the standard finger cursor. (Does not apply if Active Number Mode set.)

Auto Show Errors: If checked, as you enter a number in a cell, it will display in red if incorrect.

Auto Remove Pencil marks: If checked, when you enter a final (pen) number in a cell, that number will be automatically removed from the possibles in all other cells in same row, column or block.

You can also customize the color of the grid and the numbers.

#### Solve Menu

Main options to aid in solving puzzles.
##### Check My Solution
Checks to see if you have solved the puzzle correctly. Any errors made will be shown in red.
##### Hint
Suggests which cell may be the next easiest to solve. It will not fill in the value - for that you need to select the "Solve One Cell" option.
##### Clue
If a cell is solvable via basic solving techniques, then the clue will suggest you look where a particular number is located in a block, row or column and will highlight that area of the grid. This helps you more than the "Hint" option and is the easiest aid you can ask for, save getting the actual answer.

If the only way to solve a cell is via more than one step using Sandwich total solving techniques, then the clue will point you to the cell and you may need to resort to the "Solve One Cell" if still stuck.

##### Solve One Cell
This is a very powerful option, especially as a learning tool. It will fill in one of the cells and displays the reason why that number is the answer to the cell. If the software took multiple steps to solve the cell, it will offer a walkthrough to show you the steps it took. Sometimes it may show additional steps that you could have avoided looking at it as "a human".
##### Possibles Basic
This option will show you the possible numbers for each unsolved cell using the most basic logic technique ie it looks at what numbers are already present in the same block, row and column.
##### Possibles Sandwich
This option uses the Sandwich total numbers to further reduce the possibles for each unsolved cell. Note that the puzzles currently do not use the hard regular Sudoku strategies such as naked pairs, block line pointing, x-wing etc.
##### Solve
Shows the completed solution.