SudokuSolver Forum http://www.rcbroughton.co.uk/sudoku/forum/ |
|
Trying to wrap my brain around ERs http://www.rcbroughton.co.uk/sudoku/forum/viewtopic.php?f=10&t=1066 |
Page 1 of 1 |
Author: | enxio27 [ Fri Oct 26, 2012 4:15 pm ] |
Post subject: | Trying to wrap my brain around ERs |
Here's the grid as it stands: Code: .-------------------------------.-------------------------------.-------------------------------. | 2 4 78 | 6 3 57 | 9 1 578 | | 3 79 6 | 489 4578 1 | 25 78 278 | | 19 5 178 | 89 78 2 | 4 6 3 | :-------------------------------+-------------------------------+-------------------------------: | 19 379 17 | 2 578 4 | 35 78 6 | | 6 37 2 | 38 9 57 | 1 4 578 | | 5 8 4 | 13 17 6 | 23 9 27 | :-------------------------------+-------------------------------+-------------------------------: | 8 1 9 | 5 6 3 | 7 2 4 | | 7 2 3 | 14 14 8 | 6 5 9 | | 4 6 5 | 7 2 9 | 8 3 1 | '-------------------------------.-------------------------------.-------------------------------' Sudoku Solver shows this hint: 741. Grid:02 Empty Rectangle on candidate 7 at n1(c3->r2) - r2c8=r4c8 Why? Apparently I'm not getting the logic here, or perhaps it's the notation. Where is the hinge, and where are the other three corners? |
Author: | HATMAN [ Sat Oct 27, 2012 12:16 pm ] |
Post subject: | Re: Trying to wrap my brain around ERs |
If you do F10 it becomes clear: The 7 at r4c3 eliminates the 7s in r13c3 forcing r2c2 and it also eliminates the 7 at r4c8 forcing r2c8 - conflict. I agree the notation is hard to understand. Note with Ed's ordering JSudoku give a very obvious two-string kite on 8. |
Author: | nj3h [ Sun Oct 28, 2012 6:20 pm ] |
Post subject: | Re: Trying to wrap my brain around ERs |
1. Look at row 5. 2. Note there are two cells with an 8 pencil mark. 3. If r5c9 is an 8, then r1c9 and r2c9 cannot be an 8. 4. Then r2c8 is an 8 and r2c4 is not an 8. 5. Now let's look at the other 8 in row 5 (r5c4). 6. If this cell is an 8, then r2c4 cannot be an 8. 7. Therefore, whichever cell in row 5 is an 8 yields the situation where r2c4 can never be an 8. Therefore candidate 8 can be removed from r2c4. I don't know if this is enough to solve the puzzle, but the ER technique works like this. Some things to thing about: Notice the two 8s in r5 are in different blocks. There must be only 2 candidates with the same value (in this case 8). There are 8s still unplaced in blocks 2 and 3. Without these two situations the ER just won't work. Good luck with this. |
Author: | enxio27 [ Fri Nov 02, 2012 3:11 pm ] |
Post subject: | Re: Trying to wrap my brain around ERs |
I finally got it. The logic seems backward from what I'm used to, and I think that's what made the concept difficult. This explanation on The New Sudoku Players' Forum finally got me through it: daj95376 wrote: Empty Rectangle:
A) A line (row/column) with two cells for a candidate. In this case, r2c8 and r4c8 in [c8]. B) A box where the candidate is confined to one row and one column. In this case, [r2] and [c3] in [b1]. C) One candidate in (A) exists in one line from (B). In this case, r2c8 in [r2]. D)) An elimination can occur in the cell that's in the alternate line of (B) and also sees the alternate cell of (A). In this case, r4c3 is in [c3] and sees r4c8. |
Page 1 of 1 | All times are UTC |
Powered by phpBB® Forum Software © phpBB Group https://www.phpbb.com/ |