Re: Killer Sudoku 15 January 2021

paulv66 wrote:

This was another real toughie. It took me quite a while to get a hook into it, although it fell into place after that. Be interesting to see how many people in total solve it.

Here is my method for solving this puzzle. I found it to be an interesting puzzle to solve.

1. Calculate cage values

b9=7,9

g6=6,8,9

i6=6,7,8,9

2. Add row 9

>> a9+d9=8

>> a9 & d9=2,3,5,6

3. Cage e9 must have 8, it is the only cage in row 9 that can have 8

4. g9,h9,i9 can not be 8 (refer to cages g6,i6: both g6 and i6 would be 8)

>> e9 or f9 must be 8

5. g7,g8,i7 can not be 6,8,9 (by adding cages in the 3x3 box e9+f9 would have to total 8)

>> i7=7

6. Using same method as step 5

g6 is not 9

7. Add columns f,g,h,i

>> e1,e7,e9 = 6,8,9

8. Add 3x3 box (g7:i9)

>> e9+f9=9

>> e9=8, f9=1

9. Calculate cage values

i2=6,9

i4=1,2,4,5

g5=2,4,7,9

10. Cage h5 must have 2 or 4

>> cage i4 can not be 2,4

11. Calculate cage values

h7=1,2,3,4,5,6

cage e9: g9=2,3,4,5 h9=3,4,5,6 i9=2,3,4

12. Calculate cage values

h3=2,3,7,8

(note in column h 1 must be in h7 or h8)

13. Cage g5 must be 2,9 (only cage with 9 in 3x3 box)

14. Calculate cage values

h3=3,7 (refer to cage h5)

e1 each cell can be all available values

b1 =4,5,6,7,8,9

15. g4 & g5=3,4,7 (note that g4 or g5=4)

16. Cage b2 is not 4,9 (cage e1 would have no possible values)

(note h2 would be 4 if cage b2=4,9)

17. Add row 1

>> a1+d1=h2+1

>> a1+d1=5,6 or 9

>> a1,d1=1,2,3,4,5,6,7,8

18. Add 3x3 box (a7:c9)

>> a7+c7+c8=8

a7=3,5 c7&c8=1,2,4

(note c7 or c8 must be 1)

19. In column d the only cell that could be 9 is d5

20. g5=2, g6=9, a6=7, a7=5

c7&c8=1,2

21. Add 3x3 box (d7:f9)

>> d7=c8+2

>> d7=3,4

22. d8,e8 or d9 must be 2

>> c8 is not 2

>> c7=2, d7=3, d6=4

From this point it is all basic steps to complete the puzzle.