DKM Sudoku Online Help


How To Play

Sudoku is a puzzle with a grid containing nine large blocks. Each block is divided into its own matrix of nine cells. The rules for solving Sudoku puzzles are very simple: 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. When you've filled the entire grid, the puzzle is solved.
  • To play a new puzzle, touch the "New" button and select a difficulty level from the menu. (You need to be online to get a puzzle.) You can also enter a puzzle from another source (eg newspaper)- follow the onscreen instructions.
  • Fill in blanks with the Pen (touch the number you want to enter and then the cell).
  • To clear a cell, select the "C" key, or enter the same number again. So, if you touch a cell with the incorrect number selected, touch again to clear.
  • 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, touch the "Pencil" icon to be placed in "Pencil mode".
  • You may enter as many pencil marks as you like in each cell.
  • Touch the "Pencil" icon again to return to "Pen" mode.
  • Touch the Undo icon (yellow arrow) to undo last input. You can undo all the way back to the beginning.
  • To remove just one pencilled number in a cell, enter that number again.


Active Number Mode

If this is checked, then you first select a number from the number panel and it becomes the "active" number. Then touching a cell will fill it with this number. This mode is preferred if you like to work on one number at a time. If Active Number Mode is off, then you first select a cell and then touch the number on the number panel you wish to enter in that cell.

When Select Number Hilite All Its Cells

If checked, when you touch a number on the number panel, all cells with that number already entered will be highlighted.

Auto Remove Pencil Marks

If checked, when you enter a final (pen) number into a cell, all cells in that row/col/block will remove any pencil number the same.

De-emphasize Completed Numbers:

If checked, when all 9 of a number have been entered correctly, that number will be de-emphasized on the Number Panel. You can still select the number, though.

Color Setting

This is self explanatory. When you touch the color field in the Preferences Form, you can either touch the desired color or enter its six character hex value.


The scoring system in DKM Sudoku is unique and attempts to provide a uniform measure of your performance across all puzzles, including the ones you input manually from other sources. The score is calculated when you complete the puzzle (unless ineligible - see section below) according to the following formula:

Score = Rating + TimeBonus - Accuracy - SolveAids

  • Rating = the rating index assigned to each puzzle. This index attempts to measure the difficulty of the puzzle by examining at each stage of the solving process how many cells can be solved by logic relative to the number of unsolved cells. It also looks at what techniques are required to solve those cells. Those that rely on more sophisticated techniques greatly increase the rating index. The current difficulty level (Easy, Medium, Hard, Tough) is only based on the techniques required to solve and you may find that some Easy puzzles have a higher rating than other Medium ones or similarly for Medium/Hard/Tough.
  • TimeBonus = extra points for completing the puzzle quickly. In fact, time is still the most important factor determining your score. The time bonus is computed by taking the average time per difficulty level divided by your time and then multiplied by the rating index. For example, the average time for Medium puzzles is currently set at 12 minutes (720 seconds) so if you complete a puzzle with a rating of 1100 in 6 minutes, you will score a time bonus of (720/360 * 1100), ie 2200 which is twice the rating for that puzzle. If you completed the puzzle in 20 minutes (1200 seconds), your time bonus would be (720/1200 * 1100) ie 660.
  • Accuracy = the number of errors you make. Errors are only recorded when you enter an incorrect value and then enter a value in another cell. So, if you accidentally enter an incorrect number and immediately correct it, no error will be recorded. For the first error you lose 30 points, for each subsequent error the points lost increases by 10. So you would lose 40 points for the second error and so on. Note that pencil marks do not affect the scoring in any way.
  • SolveAids = each time you use a hint or clue or check your input. You lose 40 points for each hint, 50 for each clue and 20 each time you check your input.

Scoring Ineligibility

If any of the following are true, you will not receive a score for that puzzle.
  • You use the "Solve", "Solve One Cell" or "Possibles" options from the Solve menu.
  • You save the puzzle and then reload.
  • You do not complete the puzzle.

Menu Options

New Menu

Select a new puzzle from one of the difficulty levels. For "Easy" and "Medium" puzzles, a new one is available every minute. For "Hard" puzzles, a new one is available every hour. For "Tough" puzzles, a new one is available every day.
All puzzles are solvable by pure logic - no guessing required!

You can also enter a puzzle from an external source. After entering all the fixed numbers, touch the Done button.

If you know a puzzle number (perhaps given by a friend), you also play the puzzle by selecting the "Enter Archive Puzzle#".

Edit Menu

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.
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.
Loads the last saved puzzle on this computer.
Saves the current state of the puzzle to temporary user data on this phone. 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.

Solve Menu

Main options to aid in solving puzzles.
Checks to see if you have solved the puzzle correctly. Any errors made will be shown in red.
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.
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 advanced solving techniques (as found in Hard and Tough puzzles), then the clue will point you to the cell and say what technique(s) is/are required. This is not as helpful 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. In the case of advanced techniques, it will walk through the steps to solve the cell. Sometimes there may be additional steps shown which are not necessary for the solving of that cell but they offer a useful practice tool.
This option will show you the possible numbers for each unsolved cell only using logic techniques applicable to puzzle level.
Solves the puzzle and shows the completed solution.