Abs wrote:This Friday's(16 Dec) tough sudoku:
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- - -|- 9 -|- - 3
- - -|- - 2|9 1 4
- - -|8 - -|6 - -
-----------------
- 4 -|7 - 9|- 5 8
- - -|- - -|- - -
7 3 -|1 - 5|- 2 -
-----------------
- - 5|- - 3|- - -
1 7 4|6 - -|- - -
9 - -|- 4 -|- - -
I could only put in 6 numbers, can someone tell me what techiques you used(and when) to solve this puzzle.
Abs,
First some basic steps: ( I suspect you got these, but here they are anyway)
R6C7 = 4 therefore R7C8=4.
R9C3=3
R7C4=9
then notice these Naked singles:
R8C6=8,
R9C8=6,
R3C8=7, which leads to R1C8=8.
then we have the following grid.
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. . . | . 9 . | . 8 3
. . . | . . 2 | 9 1 4
. . . | 8 . . | 6 7 .
-------+-------+------
. 4 . | 7 . 9 | . 5 8
. . . | . . . | . . .
7 3 . | 1 . 5 | 4 2 .
-------+-------+------
. . 5 | 9 . 3 | . 4 .
1 7 4 | 6 . 8 | . . .
9 . 3 | . 4 . | . 6 .
with candidate grid:
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2456 1256 1267 | 45 9 67 | 25 8 3
3568 568 678 | 35 67 2 | 9 1 4
2345 1259 129 | 8 135 14 | 6 7 25
--------------------+------------------+----------------
26 4 126 | 7 236 9 | 13 5 8
2568 125689 12689 | 234 2368 46 | 137 39 1679
7 3 689 | 1 68 5 | 4 2 69
--------------------+------------------+----------------
268 268 5 | 9 127 3 | 1278 4 127
1 7 4 | 6 25 8 | 235 39 259
9 28 3 | 25 4 17 | 12578 6 1257
You will notice a pair in Box 2 of {6,7}.
Also there is a Hidden Triplet in Row 3 of {1, 3, 4} which allows some eliminations to take place giving you only one cell in Column 5 for a Certain number, ie Hidden Single.
then you have the Grid: (Spoilers Ahead!!!)
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45 1256 1267 | 45 9 1467 | 25 8 3
358 56 678 | 35 3567 2 | 9 1 4
345 1259 129 | 8 135 14 | 6 7 25
--------------------+------------------+----------------
26 4 126 | 7 236 9 | 13 5 8
58 12569 12689 | 34 2368 46 | 137 39 1679
7 3 689 | 1 68 5 | 4 2 69
--------------------+------------------+----------------
26 26 5 | 9 17 3 | 8 4 17
1 7 4 | 6 5 8 | 23 39 29
9 8 3 | 2 4 17 | 157 6 157
You will notice a naked {2,3,9} triple in Row 8, so {2, 3, 9} do not appear elsewhere in box 9.
Also Naked {2,6} pair in Column 1, so {2,6} do not appear elsewhere in Column 1.
Now there is also another Naked Pair in Row 1, so.....
This is a interesting puzzle, though it doesn't have any X-Wings it is still a hard nut to crack.