## Uniquess of Sudoku Puzzles

All about puzzles in newspapers, magazines, and books

### Uniquess of Sudoku Puzzles

Dear Pappocom

I have started to play Sudoku through a newspaper's introduction about 2weeks ago and was deeply attracted by it. Through the 2 week's playing, I could solve all the puuzles that I played (inculde some tough ones that were raised by some players in this forum) except one (raised by Bernard Stay's Difficult Tues. 12 July on 12 July which I wondered if there was some mistake in the puzzle shown in forum). I believe that the logical techiques that I have deducted in these 2 weeks during my puzzle playing should be able to allow me to solve all the Sudoku puzzles (but not the killer's ones that I still have not played any one yet) provided it is solvable and has an unique solution based on the hints showned regardless its difficult rating. But I still have the following queries :

1. How could you set up a proper Sudoku puzzle, i.e how could you make sure the puzzle is solvable and will have only 1 unique solution? My logical deductions could only allow me to get the answer at the end of the playing, i.e. either get an inique solution and indicates that there will be no solution or more than 1 solution but not able to help me to set up a proper Sudoku puzzle at the beginning before the playing.

2. How could you rate the grade of the diffiuclty of a Sudoku puzzle. Need you to play the puzzle before your rate it? But I don't think so and is surprise how you could rate the grade of the diffiuclty.

Hope that you could satisfy my curiosity because I was addicted to the game. By the way, do you know where could I buy a Sudoku puzzle book in Hong Kong. Our newspapaers provide only 1 puzzle/day here.

Lyh4828
lyh4828

Posts: 4
Joined: 03 September 2005

Sorry, some typing mistakes. The correct one should be read as follows :

Dear Pappocom

I have started to play Sudoku through a newspaper's introduction about 2weeks ago and was deeply attracted by it. Through the 2 week's playing, I could solve all the puuzles that I played (inculde some tough ones that were raised by some players in this forum) except one (raised by Bernard Stay's Difficult Tues. 12 July on 12 July which I wondered if there was some mistake in the puzzle shown in forum). I believe that the logical techiques that I have deducted in these 2 weeks during my puzzle playing should be able to allow me to solve all the Sudoku puzzles (but not the killer's ones that I still have not played any one yet) provided it is solvable and has an unique solution based on the hints showned regardless its difficult rating. But I still have the following queries :

1. How could you set up a proper Sudoku puzzle, i.e how could you make sure the puzzle is solvable and will have only 1 unique solution? My logical deductions could only allow me to get the answer at the end of the playing, i.e. either get an inique solution or indicates that there will be no solution or more than 1 solution but not able to help me to set up a proper Sudoku puzzle at the beginning before the playing.

2. How could you rate the grade of the diffiuclty of a Sudoku puzzle. Need you to play the puzzle before your rate it? But I don't think so and is surprise how you could rate the grade of the diffiuclty properly and logically.

Hope that you could satisfy my curiosity because I was addicted to the game. By the way, do you know where could I buy a Sudoku puzzle book in Hong Kong? Our newspapaers provide only 1 puzzle/day here.

Lyh4828
lyh4828

Posts: 4
Joined: 03 September 2005

I don't know for sure but i bnelieve that they are made backwards from a finished article, i made one once but it was really really easy, the difficult ones require knowledge of different techniques and so these i assume are incorporated when they are made.

My puzzle:

**3**6*89
9*617**5*
*572*314*
7**5***64
*14*298**
*8**4*3*2
*6**3*5*7
3***1462*
298******
Pi

Posts: 389
Joined: 27 May 2005

Dear Pi,

Thanks for your nice suggestion and IU really appreciate that. Yes, to work backwords from a finished one a way that we could set up a Sudiku puzzle that should be solvable. But is it really that way that they work right now, I wonder because it is rather clumpsy and tedious. Besides, i still have the following queries :

1. How many and where should we put down the hints to make sure it will lead to a unique solution (if not putting down enough hints and at the proper positions, I just wonder if it will lead to multiple soultions.

2. How could one evaluate or determine the degree of dicfficulty with a proper and reasonable rating?

Pi, could you try Bernard Stay's Tue. July 12 puzzle? I feel that based on what Bernard has reached, there is no unique solution to the puzzle. So, I just wonder if Bernard has made any mistake in his puzzle. I get no reply from Bernard nor Pappocom and just wonder if you could rtry and tell me your result.

The solution to your puzzle is :

123 456 789
946 178 253
857 293 146
732 581 964
614 329 875
589 647 312
461 832 597
375 914 623
298 765 431

Look forward to hearing from you soon

Lyh4828
lyh4828

Posts: 4
Joined: 03 September 2005

lyh4828 wrote:

Pi, could you try Bernard Stay's Tue. July 12 puzzle? I feel that based on what Bernard has reached, there is no unique solution to the puzzle. So, I just wonder if Bernard has made any mistake in his puzzle. I get no reply from Bernard nor Pappocom and just wonder if you could rtry and tell me your result.

Lyh4828

Bernard did finish the puzzle after spotting the 6/9 pair in column 7.
possum

Posts: 86
Joined: 05 April 2005

### Uniqueness of SuDoku puzzles

Puzzle 346 in Monday's Times had 2 solutions. Each of the numbers 4 and 7 in rows 4,5,6 and 7 (or, if you prefer, columns 3,5,6, and 7) could be switched from the published solution. So, not a unique answer on this occasion....................
Guest

Posts: 312
Joined: 25 November 2005

Actually, the 7 in r7c6 is a clue number, so you can't move it.
PaulIQ164

Posts: 533
Joined: 16 July 2005

### Uniquess of Sudoku Puzzles

Ah, the perils of working from a manually copied version rather than the original!
Guest

Posts: 312
Joined: 25 November 2005