Sudoku Solution No. 17

Hard Score 71 / 100
Digits appear one by one.

Step-by-step solution

Steps 64 Estimated time 65 – 98 min Hardest technique Box/Line Clues 23
Given digit (clue) Solved digit Placement (✓ RlCc=d) Elimination (✗ RlCc≠d)
1 Naked Single ✓ R9C2=5
Look at cell R9C2. Every other digit already appears in its row, column or box. Only one option remains: R9C2 = 5.
2 Naked Single ✓ R9C7=1
Look at cell R9C7. Every other digit already appears in its row, column or box. Only one option remains: R9C7 = 1.
3 Naked Single ✓ R9C1=6
Look at cell R9C1. Every other digit already appears in its row, column or box. Only one option remains: R9C1 = 6.
4 Hidden Single ✓ R4C6=4
Scan the empty cells in this box where 4 could go. Across the whole box, 4 has only one possible spot left. So R4C6 = 4.
5 Hidden Single ✓ R5C4=1
Scan the empty cells in this box where 1 could go. Across the whole box, 1 has only one possible spot left. So R5C4 = 1.
6 Hidden Single ✓ R5C6=6
Scan the empty cells in this column where 6 could go. Across the whole column, 6 has only one possible spot left. So R5C6 = 6.
7 Hidden Single ✓ R6C9=6
Scan the empty cells in this box where 6 could go. Across the whole box, 6 has only one possible spot left. So R6C9 = 6.
8 Hidden Single ✓ R8C4=6
Scan the empty cells in this row where 6 could go. Across the whole row, 6 has only one possible spot left. So R8C4 = 6.
9 Hidden Single ✓ R8C5=1
Scan the empty cells in this box where 1 could go. Across the whole box, 1 has only one possible spot left. So R8C5 = 1.
10 Hidden Single ✓ R8C2=2
Scan the empty cells in this row where 2 could go. Across the whole row, 2 has only one possible spot left. So R8C2 = 2.
11 Hidden Single ✓ R1C5=2
Scan the empty cells in this box where 2 could go. Across the whole box, 2 has only one possible spot left. So R1C5 = 2.
12 Hidden Single ✓ R2C5=8
Scan the empty cells in this box where 8 could go. Across the whole box, 8 has only one possible spot left. So R2C5 = 8.
13 Hidden Single ✓ R3C7=2
Scan the empty cells in this box where 2 could go. Across the whole box, 2 has only one possible spot left. So R3C7 = 2.
14 Hidden Single ✓ R4C5=5
Scan the empty cells in this box where 5 could go. Across the whole box, 5 has only one possible spot left. So R4C5 = 5.
15 Hidden Single ✓ R4C8=1
Scan the empty cells in this box where 1 could go. Across the whole box, 1 has only one possible spot left. So R4C8 = 1.
16 Hidden Single ✓ R4C9=2
Scan the empty cells in this box where 2 could go. Across the whole box, 2 has only one possible spot left. So R4C9 = 2.
17 Hidden Single ✓ R5C3=2
Scan the empty cells in this box where 2 could go. Across the whole box, 2 has only one possible spot left. So R5C3 = 2.
18 Hidden Single ✓ R6C1=5
Scan the empty cells in this box where 5 could go. Across the whole box, 5 has only one possible spot left. So R6C1 = 5.
19 Hidden Single ✓ R6C4=2
Scan the empty cells in this row where 2 could go. Across the whole row, 2 has only one possible spot left. So R6C4 = 2.
20 Hidden Single ✓ R7C4=5
Scan the empty cells in this box where 5 could go. Across the whole box, 5 has only one possible spot left. So R7C4 = 5.
21 Hidden Single ✓ R7C6=2
Scan the empty cells in this box where 2 could go. Across the whole box, 2 has only one possible spot left. So R7C6 = 2.
22 Naked Single ✓ R4C3=3
Look at cell R4C3. Every other digit already appears in its row, column or box. Only one option remains: R4C3 = 3.
23 Naked Single ✓ R5C5=3
Look at cell R5C5. Every other digit already appears in its row, column or box. Only one option remains: R5C5 = 3.
24 Naked Single ✓ R6C2=7
Look at cell R6C2. Every other digit already appears in its row, column or box. Only one option remains: R6C2 = 7.
25 Naked Single ✓ R6C8=3
Look at cell R6C8. Every other digit already appears in its row, column or box. Only one option remains: R6C8 = 3.
26 Hidden Single ✓ R1C9=1
Scan the empty cells in this column where 1 could go. Across the whole column, 1 has only one possible spot left. So R1C9 = 1.
27 Hidden Single ✓ R3C2=1
Scan the empty cells in this row where 1 could go. Across the whole row, 1 has only one possible spot left. So R3C2 = 1.
28 Naked Pair ✗ 2 eliminations
Spot R8C1 and R8C9 on this row. These two cells can only hold 3 and 4: they reserve those digits. 3 and 4 are therefore removed from the other cells of the row.
29 Pointing ✗ 1 elimination
Look at where 4 can go in this box. All its spots lie on a single column (R7C9 and R8C9). 4 is therefore removed from that column outside the box.
30 Box/Line ✗ 7 eliminations
(1) Look at where 7 can go on this row. (2) Look at where 4 can go on this column. (1) All its spots lie within a single box (R2C7 and R2C8). (2) All its spots lie within a single box (R1C3, R2C3 and R3C3). (1) 7 is therefore removed from the rest of the box. (2) 4 is therefore removed from the rest of the box.
31 Naked Pair ✗ 5 eliminations
Spot R2C2 and R2C9 on this row. These two cells can only hold 3 and 9: they reserve those digits. 3 and 9 are therefore removed from the other cells of the row.
32 Naked Single ✓ R2C4=4
Look at cell R2C4. Every other digit already appears in its row, column or box. Only one option remains: R2C4 = 4.
33 Skyscraper ✗ 3 eliminations
Find 3 on two rows, each with exactly two candidate positions. A shared column connects one end of each pair. Whichever way the logic falls, one of the two free ends must hold 3. R1C1, R3C1 and R7C2 is seen by both free ends: 3 is therefore eliminated there.
34 Naked Single ✓ R7C2=4
Look at cell R7C2. Every other digit already appears in its row, column or box. Only one option remains: R7C2 = 4.
35 Naked Single ✓ R8C1=3
Look at cell R8C1. Every other digit already appears in its row, column or box. Only one option remains: R8C1 = 3.
36 Naked Single ✓ R8C9=4
Look at cell R8C9. Every other digit already appears in its row, column or box. Only one option remains: R8C9 = 4.
37 Hidden Single ✓ R1C4=9
Scan the empty cells in this box where 9 could go. Across the whole box, 9 has only one possible spot left. So R1C4 = 9.
38 Hidden Single ✓ R3C4=3
Scan the empty cells in this row where 3 could go. Across the whole row, 3 has only one possible spot left. So R3C4 = 3.
39 Hidden Single ✓ R5C1=4
Scan the empty cells in this row where 4 could go. Across the whole row, 4 has only one possible spot left. So R5C1 = 4.
40 Skyscraper ✗ 1 elimination
Find 9 on two rows, each with exactly two candidate positions. A shared column connects one end of each pair. Whichever way the logic falls, one of the two free ends must hold 9. R5C8 is seen by both free ends: 9 is therefore eliminated there.
41 Hidden Single ✓ R1C8=4
Scan the empty cells in this box where 4 could go. Across the whole box, 4 has only one possible spot left. So R1C8 = 4.
42 Hidden Single ✓ R2C2=9
Scan the empty cells in this box where 9 could go. Across the whole box, 9 has only one possible spot left. So R2C2 = 9.
43 Hidden Single ✓ R3C8=9
Scan the empty cells in this column where 9 could go. Across the whole column, 9 has only one possible spot left. So R3C8 = 9.
44 Hidden Single ✓ R4C1=9
Scan the empty cells in this box where 9 could go. Across the whole box, 9 has only one possible spot left. So R4C1 = 9.
45 Hidden Single ✓ R5C7=9
Scan the empty cells in this box where 9 could go. Across the whole box, 9 has only one possible spot left. So R5C7 = 9.
46 Hidden Single ✓ R7C7=3
Scan the empty cells in this box where 3 could go. Across the whole box, 3 has only one possible spot left. So R7C7 = 3.
47 Hidden Single ✓ R7C9=9
Scan the empty cells in this box where 9 could go. Across the whole box, 9 has only one possible spot left. So R7C9 = 9.
48 Naked Single ✓ R2C9=3
Look at cell R2C9. Every other digit already appears in its row, column or box. Only one option remains: R2C9 = 3.
49 Naked Single ✓ R3C1=7
Look at cell R3C1. Every other digit already appears in its row, column or box. Only one option remains: R3C1 = 7.
50 Naked Single ✓ R3C6=5
Look at cell R3C6. Every other digit already appears in its row, column or box. Only one option remains: R3C6 = 5.
51 Naked Single ✓ R4C7=8
Look at cell R4C7. Every other digit already appears in its row, column or box. Only one option remains: R4C7 = 8.
52 Naked Single ✓ R5C2=8
Look at cell R5C2. Every other digit already appears in its row, column or box. Only one option remains: R5C2 = 8.
53 Naked Single ✓ R5C8=7
Look at cell R5C8. Every other digit already appears in its row, column or box. Only one option remains: R5C8 = 7.
54 Naked Single ✓ R8C7=5
Look at cell R8C7. Every other digit already appears in its row, column or box. Only one option remains: R8C7 = 5.
55 Naked Single ✓ R8C8=8
Look at cell R8C8. Every other digit already appears in its row, column or box. Only one option remains: R8C8 = 8.
56 Naked Single ✓ R1C1=8
Look at cell R1C1. Every other digit already appears in its row, column or box. Only one option remains: R1C1 = 8.
57 Naked Single ✓ R1C2=3
Look at cell R1C2. Every other digit already appears in its row, column or box. Only one option remains: R1C2 = 3.
58 Naked Single ✓ R1C6=7
Look at cell R1C6. Every other digit already appears in its row, column or box. Only one option remains: R1C6 = 7.
59 Naked Single ✓ R1C7=6
Look at cell R1C7. Every other digit already appears in its row, column or box. Only one option remains: R1C7 = 6.
60 Naked Single ✓ R2C7=7
Look at cell R2C7. Every other digit already appears in its row, column or box. Only one option remains: R2C7 = 7.
61 Naked Single ✓ R2C8=5
Look at cell R2C8. Every other digit already appears in its row, column or box. Only one option remains: R2C8 = 5.
62 Naked Single ✓ R3C3=4
Look at cell R3C3. Every other digit already appears in its row, column or box. Only one option remains: R3C3 = 4.
63 Naked Single ✓ R1C3=5
Look at cell R1C3. Every other digit already appears in its row, column or box. Only one option remains: R1C3 = 5.
64 Naked Single ✓ R2C3=6
Look at cell R2C3. Every other digit already appears in its row, column or box. Only one option remains: R2C3 = 6.