Stuck on a really hard sudoku!

jkmyoung

Hey, are there any sudoku experts out there? Can anyone tell me the next step in solving this sudoku and explain it properly? I've used all the rules I can think of but am now stuck.

Expand|Select|Wrap|Line Numbers

 
51--263--

7264-35-8

93-5-76--

395278461

86--54--9

47--698-5

-59-41-83

-43--2-5-

-87-35-4-

JosAH

A stupid brute force solver solves this one in 0ms.

Expand|Select|Wrap|Line Numbers

 
+-------+-------+-------+

| 5 1 4 | 8 2 6 | 3 9 7 | 

| 7 2 6 | 4 9 3 | 5 1 8 | 

| 9 3 8 | 5 1 7 | 6 2 4 | 

+-------+-------+-------+

| 3 9 5 | 2 7 8 | 4 6 1 | 

| 8 6 1 | 3 5 4 | 2 7 9 | 

| 4 7 2 | 1 6 9 | 8 3 5 | 

+-------+-------+-------+

| 2 5 9 | 6 4 1 | 7 8 3 | 

| 1 4 3 | 7 8 2 | 9 5 6 | 

| 6 8 7 | 9 3 5 | 1 4 2 | 

+-------+-------+-------+

kind regards,

Jos

jkmyoung

Thanks to your help I've found that there are at least 2 other solutions.

Expand|Select|Wrap|Line Numbers

 
+-------+-------+-------+ 

| 5 1 8 | 9 2 6 | 3 7 4 | 

| 7 2 6 | 4 1 3 | 5 9 8 | 

| 9 3 4 | 5 8 7 | 6 1 2 | 

+-------+-------+-------+ 

| 3 9 5 | 2 7 8 | 4 6 1 | 

| 8 6 - | - 5 4 | 7 - 9 | 

| 4 7 - | - 6 9 | 8 - 5 | 

+-------+-------+-------+ 

| 6 5 9 | 7 4 1 | 2 8 3 | 

| 1 4 3 | 8 9 2 | 1 5 7 | 

| 2 8 7 | 6 3 5 | 9 4 6 | 

+-------+-------+-------+

JosAH

Quote:

Originally Posted by jkmyoung

Thanks to your help I've found that there are at least 2 other solutions.

Yup, and that's exactly why trying to compute a solution fails: sometimes you can not compute a single value for a cell, only two or more values are possible. e.g. see an empty sudoku board. A (more or less) brute force approach simply tries a possiblity and when it fails it tries another possibility.

Let's continue this discussion in the original thread in the algorithms section.

kind regards,

Jos

Stuck on a really hard sudoku!

re: Stuck on a really hard sudoku!

re: Stuck on a really hard sudoku!

re: Stuck on a really hard sudoku!

Similar Misc bytes

/bytes/development

/bytes/it

/bytes/about