Sudoku Solution No. 9

Hard Score 71 / 100
Digits appear one by one.

Step-by-step solution

Steps 64 Estimated time 104 – 156 min Hardest technique X-Wing Clues 24
Given digit (clue) Solved digit Placement (✓ RlCc=d) Elimination (✗ RlCc≠d)
1 Hidden Single ✓ R1C6=6
Scan the empty cells in this box where 6 could go. Across the whole box, 6 has only one possible spot left. So R1C6 = 6.
2 Hidden Single ✓ R5C2=8
Scan the empty cells in this row where 8 could go. Across the whole row, 8 has only one possible spot left. So R5C2 = 8.
3 Hidden Single ✓ R6C4=6
Scan the empty cells in this row where 6 could go. Across the whole row, 6 has only one possible spot left. So R6C4 = 6.
4 Hidden Single ✓ R7C8=6
Scan the empty cells in this column where 6 could go. Across the whole column, 6 has only one possible spot left. So R7C8 = 6.
5 Hidden Single ✓ R8C5=8
Scan the empty cells in this row where 8 could go. Across the whole row, 8 has only one possible spot left. So R8C5 = 8.
6 Hidden Single ✓ R8C7=5
Scan the empty cells in this row where 5 could go. Across the whole row, 5 has only one possible spot left. So R8C7 = 5.
7 Hidden Single ✓ R9C1=9
Scan the empty cells in this column where 9 could go. Across the whole column, 9 has only one possible spot left. So R9C1 = 9.
8 Hidden Single ✓ R9C4=5
Scan the empty cells in this column where 5 could go. Across the whole column, 5 has only one possible spot left. So R9C4 = 5.
9 Hidden Single ✓ R9C5=6
Scan the empty cells in this box where 6 could go. Across the whole box, 6 has only one possible spot left. So R9C5 = 6.
10 Hidden Single ✓ R9C2=3
Scan the empty cells in this row where 3 could go. Across the whole row, 3 has only one possible spot left. So R9C2 = 3.
11 Naked Pair ✗ 13 eliminations
(1) Spot R5C1 and R5C4 on this row. (2) Spot R5C1 and R6C2 in this box. (1) These two cells can only hold 1 and 7: they reserve those digits. (2) These two cells can only hold 1 and 7: they reserve those digits. (1) 1 and 7 are therefore removed from the other cells of the row. (2) 1 and 7 are therefore removed from the other cells of the box.
12 Hidden Single ✓ R5C5=2
Scan the empty cells in this box where 2 could go. Across the whole box, 2 has only one possible spot left. So R5C5 = 2.
13 Hidden Single ✓ R5C6=4
Scan the empty cells in this column where 4 could go. Across the whole column, 4 has only one possible spot left. So R5C6 = 4.
14 Hidden Single ✓ R3C6=2
Scan the empty cells in this column where 2 could go. Across the whole column, 2 has only one possible spot left. So R3C6 = 2.
15 Naked Pair ✗ 5 eliminations
Spot R3C3 and R8C3 on this column. These two cells can only hold 1 and 7: they reserve those digits. 1 and 7 are therefore removed from the other cells of the column.
16 Naked Single ✓ R9C3=4
Look at cell R9C3. Every other digit already appears in its row, column or box. Only one option remains: R9C3 = 4.
17 Naked Single ✓ R9C9=1
Look at cell R9C9. Every other digit already appears in its row, column or box. Only one option remains: R9C9 = 1.
18 Hidden Single ✓ R1C2=4
Scan the empty cells in this column where 4 could go. Across the whole column, 4 has only one possible spot left. So R1C2 = 4.
19 Hidden Single ✓ R2C5=4
Scan the empty cells in this row where 4 could go. Across the whole row, 4 has only one possible spot left. So R2C5 = 4.
20 Hidden Single ✓ R1C9=5
Scan the empty cells in this box where 5 could go. Across the whole box, 5 has only one possible spot left. So R1C9 = 5.
21 Hidden Single ✓ R2C9=2
Scan the empty cells in this box where 2 could go. Across the whole box, 2 has only one possible spot left. So R2C9 = 2.
22 Hidden Single ✓ R3C2=5
Scan the empty cells in this box where 5 could go. Across the whole box, 5 has only one possible spot left. So R3C2 = 5.
23 Hidden Single ✓ R4C1=5
Scan the empty cells in this box where 5 could go. Across the whole box, 5 has only one possible spot left. So R4C1 = 5.
24 Hidden Single ✓ R4C2=2
Scan the empty cells in this column where 2 could go. Across the whole column, 2 has only one possible spot left. So R4C2 = 2.
25 Hidden Single ✓ R4C3=6
Scan the empty cells in this box where 6 could go. Across the whole box, 6 has only one possible spot left. So R4C3 = 6.
26 Naked Single ✓ R2C3=8
Look at cell R2C3. Every other digit already appears in its row, column or box. Only one option remains: R2C3 = 8.
27 Naked Single ✓ R1C3=2
Look at cell R1C3. Every other digit already appears in its row, column or box. Only one option remains: R1C3 = 2.
28 Hidden Single ✓ R1C8=8
Scan the empty cells in this row where 8 could go. Across the whole row, 8 has only one possible spot left. So R1C8 = 8.
29 Hidden Single ✓ R2C1=6
Scan the empty cells in this row where 6 could go. Across the whole row, 6 has only one possible spot left. So R2C1 = 6.
30 Hidden Single ✓ R2C8=3
Scan the empty cells in this box where 3 could go. Across the whole box, 3 has only one possible spot left. So R2C8 = 3.
31 Hidden Single ✓ R4C7=4
Scan the empty cells in this box where 4 could go. Across the whole box, 4 has only one possible spot left. So R4C7 = 4.
32 Hidden Single ✓ R4C9=8
Scan the empty cells in this column where 8 could go. Across the whole column, 8 has only one possible spot left. So R4C9 = 8.
33 Hidden Single ✓ R7C9=4
Scan the empty cells in this box where 4 could go. Across the whole box, 4 has only one possible spot left. So R7C9 = 4.
34 Naked Pair ✗ 4 eliminations
Spot R2C4 and R5C4 on this column. These two cells can only hold 1 and 7: they reserve those digits. 1 and 7 are therefore removed from the other cells of the column.
35 Pointing ✗ 1 elimination
Look at where 9 can go in this box. All its spots lie on a single row (R4C4, R4C5 and R4C6). 9 is therefore removed from that row outside the box.
36 Two-String Kite ✗ 1 elimination
Find 7 on one row and one column, each with two candidate positions, sharing a box. The two strands meet in the shared box. One of the two free ends must hold 7. R3C5 is seen by both free ends: 7 is therefore eliminated there.
37 Two-String Kite ✗ 1 elimination
Find 7 on one row and one column, each with two candidate positions, sharing a box. The two strands meet in the shared box. One of the two free ends must hold 7. R1C1 is seen by both free ends: 7 is therefore eliminated there.
38 Pointing ✗ 2 eliminations
Look at where 7 can go in this box. All its spots lie on a single row (R3C1 and R3C3). 7 is therefore removed from that row outside the box.
39 Naked Single ✓ R3C9=9
Look at cell R3C9. Every other digit already appears in its row, column or box. Only one option remains: R3C9 = 9.
40 Naked Single ✓ R6C9=7
Look at cell R6C9. Every other digit already appears in its row, column or box. Only one option remains: R6C9 = 7.
41 Naked Single ✓ R7C7=9
Look at cell R7C7. Every other digit already appears in its row, column or box. Only one option remains: R7C7 = 9.
42 Naked Single ✓ R8C8=7
Look at cell R8C8. Every other digit already appears in its row, column or box. Only one option remains: R8C8 = 7.
43 Naked Single ✓ R4C8=1
Look at cell R4C8. Every other digit already appears in its row, column or box. Only one option remains: R4C8 = 1.
44 Naked Single ✓ R6C2=1
Look at cell R6C2. Every other digit already appears in its row, column or box. Only one option remains: R6C2 = 1.
45 Naked Single ✓ R6C8=9
Look at cell R6C8. Every other digit already appears in its row, column or box. Only one option remains: R6C8 = 9.
46 Naked Single ✓ R7C2=7
Look at cell R7C2. Every other digit already appears in its row, column or box. Only one option remains: R7C2 = 7.
47 Naked Single ✓ R8C3=1
Look at cell R8C3. Every other digit already appears in its row, column or box. Only one option remains: R8C3 = 1.
48 Naked Single ✓ R8C6=9
Look at cell R8C6. Every other digit already appears in its row, column or box. Only one option remains: R8C6 = 9.
49 Naked Single ✓ R3C3=7
Look at cell R3C3. Every other digit already appears in its row, column or box. Only one option remains: R3C3 = 7.
50 Naked Single ✓ R4C6=3
Look at cell R4C6. Every other digit already appears in its row, column or box. Only one option remains: R4C6 = 3.
51 Naked Single ✓ R5C1=7
Look at cell R5C1. Every other digit already appears in its row, column or box. Only one option remains: R5C1 = 7.
52 Naked Single ✓ R5C4=1
Look at cell R5C4. Every other digit already appears in its row, column or box. Only one option remains: R5C4 = 1.
53 Naked Single ✓ R7C6=1
Look at cell R7C6. Every other digit already appears in its row, column or box. Only one option remains: R7C6 = 1.
54 Naked Single ✓ R2C4=7
Look at cell R2C4. Every other digit already appears in its row, column or box. Only one option remains: R2C4 = 7.
55 Naked Single ✓ R2C7=1
Look at cell R2C7. Every other digit already appears in its row, column or box. Only one option remains: R2C7 = 1.
56 Naked Single ✓ R4C4=9
Look at cell R4C4. Every other digit already appears in its row, column or box. Only one option remains: R4C4 = 9.
57 Naked Single ✓ R4C5=7
Look at cell R4C5. Every other digit already appears in its row, column or box. Only one option remains: R4C5 = 7.
58 Naked Single ✓ R7C5=3
Look at cell R7C5. Every other digit already appears in its row, column or box. Only one option remains: R7C5 = 3.
59 Naked Single ✓ R1C4=3
Look at cell R1C4. Every other digit already appears in its row, column or box. Only one option remains: R1C4 = 3.
60 Naked Single ✓ R1C7=7
Look at cell R1C7. Every other digit already appears in its row, column or box. Only one option remains: R1C7 = 7.
61 Naked Single ✓ R3C5=1
Look at cell R3C5. Every other digit already appears in its row, column or box. Only one option remains: R3C5 = 1.
62 Naked Single ✓ R1C1=1
Look at cell R1C1. Every other digit already appears in its row, column or box. Only one option remains: R1C1 = 1.
63 Naked Single ✓ R1C5=9
Look at cell R1C5. Every other digit already appears in its row, column or box. Only one option remains: R1C5 = 9.
64 Naked Single ✓ R3C1=3
Look at cell R3C1. Every other digit already appears in its row, column or box. Only one option remains: R3C1 = 3.