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magician
Rookie

Joined: 01 Apr 2007
Posts: 5
Location: UK

 Posted: Tue Apr 03, 2007 11:08 pm    Post subject: nice loop help please I really need help with understanding the nice loop. I am using a program to help me get used to techniques, and when im stuck ti helps me. A lot of the time the nice loop is the answer, but i am no where near getting this. Please explain the following. Please also explain in laymans terms so I get it. I would really appreciate it not to be in complex notation [/img] for example in the first one, I dont understand why the 7 is highlighted, and then again in the next cell, and then for a third time in the 3rd cell. please help me understand all the ones i have posted so i can nail these once and for all.Also how do you spot them, and how do you kno wwhich direction to go in? And how does it eliminate a candidte.
magician
Rookie

Joined: 01 Apr 2007
Posts: 5
Location: UK

mhparker
Grandmaster

Joined: 20 Jan 2007
Posts: 345
Location: Germany

GreenLantern
Regular

Joined: 30 May 2006
Posts: 14

 Posted: Wed Apr 04, 2007 11:55 pm    Post subject: Into Sudoku (from which these screenshots came) is a good program, but obviously the diagrams aren't as clear as they could be. I think the two Nice Loops that the program is trying to point out are the following: [r2c5]=7=[r1c5]-7-[r1c7]-1-[r1c1]=1=[r2c1]=7=[r2c5] => r2c5=7 [r3c2]-6-[r1c2]=6=[r1c5]=8=[r1c8]-8-[r3c9]-6-[r3c2] => r3c2<>6 In the first loop, the initial assumption is that r2c5<>7 => r1c5=7 => r1c7=1 => r1c1=3 => r2c1=1 => r2c5=7 (contradiction). Therefore, r2c5=7. The confusing part of the first diagram is that it correctly shows that r1c2=6 even though this has nothing to do with the nice loop. In the second loop, the initial assumption is r3c2=6 => r1c2=3 => r1c5=6 => r1c8=8 => r3c9=6 (contradiction). Therefore, r3c2<>6. The link that mhparker gives for the Nice Loop tutorial is a good one. In fact, I would also recommend Paul's program, SudokuXP5, as it gives excellent Nice Loop hints which include diagrams as well as the actual Nice Loop notation.
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