Kaidoku

Player, solver and creater of sudoku puzzles

Analyze a specified sudoku problem

A special position can be checked with check command followed by a position. The position is expressed with writing numbers consecutively, with blank cell expressed by 0. For example, this position

can be expressed with

310002000000860200008003075007098350090000080053620400630200900009036000000100063

When you are solving the online version of kaidoku, you can obtain the position by typing c, which copies the current position to the clipboard. Then the position can be checked with check pos [verb] where pos is the position, verb is the verbose level, which is 1 when ommitted.

check pos shows if the position has a unique solution.
check pos 2 shows a hint for basic logics (naked single and hidden single).
check pos 3 shows hints for advanced logics to determine a certain cell.
check pos 4 shows a procedure to determine a certain cell.

kaidoku-1.0.1> check 310002000000860200008003075007098350090000080053620400630200900009036000000100063

This position has a unique solution.

kaidoku-1.0.1> check 310002000000860200008003075007098350090000080053620400630200900009036000000100063 2

Look at R4C4. What number is available?

solve command shows the procedure for solving the problem completely by

solve pos [verb]

solve pos shows only the difficulty level.
solve pos 2 shows hints for trial and search.
solve pos 3 shows hints of advanced logics and result of trial and search.
solve pos 4 shows complete procedure of solving.
solve pos 5 shows whole procedure with ascii image of the board.

Alternative way to express a position

Numbers can be separated with commas ,. In this case, 9 numbers should be between the commas.
0 can be replaced with other ascii characters such as -.

Therefore following command is also available.

kaidoku-1.0.1> solve 31---2---,---86-2--,--8--3-75,--7-9835-,-9-----8-,-5362-4--,63-2--9--,--9-36---,---1---63

When you are typing a position from a printed material, this is useful because the input error is shown as to which row is invalid. For example, if you enter

kaidoku-1.0.1> solve 31---2---,---86-2--,--8--3-75,--7-9835-,-9----8-,-5362-4--,63-2--9--,--9-36---,---1---63

you get the message

Error in input: -9----8-

and you can just check this row and find that there is only 8 cells in this row. If you enter

kaidoku-1.0.1> solve 31---2---,---86-2--,--8--3-75,--7-9835-,-8-----8-,-5362-4--,63-2--9--,--9-36---,---1---63

you get a diagram and the message

Both R5C2 and R5C8 have the same value of 8.

Validity check

Sudoku is valid only when the solution is unique. If there are multiple solutions, kaidoku shows that it is invalid. For example, if you enter

kaidoku-1.0.1> solve -4-3---9-,---------,-----4236,7924--3--,----8----,--1--3627,1385-----,--------4,-7---9-6-

you get a message

Invalid sudoku with multiple solutions.

If you just want to know if the problem is valid, you can use check command and enter

kaidoku-1.0.1> check -4-3---9-,---------,-----4236,7924--3--,----8----,--1--3627,1385-----,--------4,-7---9-6-

If you want to show the multiple solutions, use solve pos 5. For example,

kaidoku-1.0.1> solve -4-3---9-,---------,-----4236,7924--3--,----8----,--1--3627,1385-----,--------4,-7---9-6- 5

It will show 2 possible solutions and common number in the 2 solutions at the end. Note that kaidoku stops looking for solutions after it finds 2 solutions. Therefore there can be more than 2 solutions. If there is no solution, for example,

kaidoku-1.0.1> solve -4-3---9-,---------,-----4236,7924--3--,4---8----,--1--3627,1385-----,--------4,-7---9-6-

then it will finally show that

Invalid sudoku with no solution.

If you want to know why there is no solution, use solve pos 5.

Example

Let us analyze this hardest sudoku. It takes several seconds to solve, depending on the power of your PC.

kaidoku-1.0.1> solve 8--------,--36-----,-7--9-2--,-5---7---,----457--,---1---3-,--1----68,--85---1-,-9----4-- 2

Search with depth 3 from R8C7.
Search with depth 3 from R7C7.
Search with depth 2 from R7C5.
Search with depth 3 from R8C9.
Search with depth 3 from R9C4.
Search with depth 1 from R6C7.
Search with depth 2 from R1C7.
Valid sudoku with unique solution of level 9 (ultimate).

It shows how extensive the search is. You can show the complete process by

kaidoku-1.0.1> solve 8--------,--36-----,-7--9-2--,-5---7---,----457--,---1---3-,--1----68,--85---1-,-9----4-- 5

Here is the result.