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Sudoku solutions should be unique
 
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boutoukoat



Joined: 16 Mar 2017
Messages: 2
Offline

A following grid has 2 solutions (swap the 5's and 2's) and therefore is not a valid one.

...5.2...
.........
.........
...2.5...
.........
.........
.........
.........
.........

These types of grid appear frequently in genina sudokus.

When I find the following combination, I exclude 5 from the possibilities at the case marked "?"

...5.2...
.........
.........
...2.?...
.........
.........
.........
.........
.........

As a result, I end-up with unsolvable sudokus. Could these invalid grids be excluded ?

This message was edited 1 time. Last update was at 16 Mar 2017 17:55:45

mxv



Joined: 29 Mar 2017
Messages: 1
Offline

you cannot exclude 5 only because it may be in a different cell. a correct solution is probably 2 up and 5 down. so, your approach cannot work and the sudoku may be solvable.
jco1986



Joined: 21 Nov 2010
Messages: 11
Offline

These puzzles all have unique solutions. If you come to a final point like this then you made an error elsewhere in the puzzle... look for it (it's there) and undo until it's undone, then re-work the puzzle.

This message was edited 1 time. Last update was at 31 Mar 2017 00:28:57

boutoukoat



Joined: 16 Mar 2017
Messages: 2
Offline

There is nothing better than an example

in the following grid, I should certainly not put a 9 here


.........
.........
.........
.........
.........
.........
.........
..1....?
..9....1

else the grid would have 2 solutions


.........
.........
.........
.........
.........
.........
.........
...1....9
...9....1


.........
.........
.........
.........
.........
.........
.........
...9....1
...1....9

Here is the probem when I filled the grid and the final solution

https://goo.gl/photos/L3JkCaxdpdApq5LH8

This sudoku has at least 4 solutions, considering this other pair where 4's and 7's can be swapped


.........
.........
.........
.........
.........
.........
.........
..4.7....
..7.4....

This message was edited 3 times. Last update was at 31 Mar 2017 19:14:09

jco1986



Joined: 21 Nov 2010
Messages: 11
Offline

This puzzle has a single solution. I've just solved it by pencil, in the order listed below. Compare to find your error.

761 429 358
249 385 176
358 761 294

473 812 965
682 594 713
195 637 842

916 253 487
524 178 639
837 946 521
jco1986



Joined: 21 Nov 2010
Messages: 11
Offline

As I said before, you've made an error elsewhere. Go back and find your error before continuing to solve the puzzle incorrectly
jco1986



Joined: 21 Nov 2010
Messages: 11
Offline

So I see what your question is.... but both instances you're questioning (the 7/4 and 9/1) are part of the given values. Thus, they're not interchangeable. Thus, there's only one, unique solution. It's not valid to interchange initial conditions.

You didn't make an error, you simply interpreted the initial conditions and solution incorrectly

This message was edited 1 time. Last update was at 1 Apr 2017 21:17:03

 
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