Classic Sudoku · 18
Classic Sudoku · 18: a 9×9 Sudoku with 36 clues and one solution. Play online, use pencil notes and hints, or compare the complete answer.
Use rows and columns: R1C1 is row 1, column 1. Enter digits inside the squares.
Read the position, one decision at a time
Follow the deductions in order. Each step uses the grid after the preceding entry.
Reveal step-by-step explanations
Deduction 1: R2C7 = 6
After the preceding deductions, row 2, column 7 has only candidate 6. Its row, column and box exclude every other digit. Enter 6, then update the remaining candidates; this conclusion does not require consulting the completed answer.
Check the existing digits: row 2: 1, 3, 4, 5, 9; column 7: 5, 8, 9; box: 2, 3, 4, 5, 7, 8, 9. Each digit already present rules out that candidate in this cell.
Deduction 2: R3C7 = 1
After the preceding deductions, row 3, column 7 has only candidate 1. Its row, column and box exclude every other digit. Enter 1, then update the remaining candidates; this conclusion does not require consulting the completed answer.
Check the existing digits: row 3: 3, 7, 8, 9; column 7: 5, 6, 8, 9; box: 2, 3, 4, 5, 6, 7, 8, 9. Each digit already present rules out that candidate in this cell.
Deduction 3: R3C1 = 6
After the preceding deductions, row 3, column 1 has only candidate 6. Its row, column and box exclude every other digit. Enter 6, then update the remaining candidates; this conclusion does not require consulting the completed answer.
Check the existing digits: row 3: 1, 3, 7, 8, 9; column 1: 2, 3, 4, 5, 7; box: 3, 5, 9. Each digit already present rules out that candidate in this cell.
Deduction 4: R3C2 = 4
After the preceding deductions, row 3, column 2 has only candidate 4. Its row, column and box exclude every other digit. Enter 4, then update the remaining candidates; this conclusion does not require consulting the completed answer.
Check the existing digits: row 3: 1, 3, 6, 7, 8, 9; column 2: 1, 2, 3, 8, 9; box: 3, 5, 6, 9. Each digit already present rules out that candidate in this cell.
Understand this position
9×9 grid · 3×3 boxes · 36 clues · 45 empty cells
Start by inspecting row 2, column 7. From the starting grid, its legal candidates are 6. Check the filled digits in that row, column and box before entering a number. Only one candidate remains: this is a naked single.
Read the complete answer by row
1 · 7 · 8 · 3 · 6 · 4 · 5 · 2 · 95 · 9 · 2 · 8 · 1 · 7 · 6 · 3 · 46 · 4 · 3 · 2 · 5 · 9 · 1 · 8 · 78 · 1 · 9 · 7 · 3 · 6 · 2 · 4 · 52 · 5 · 4 · 9 · 8 · 1 · 3 · 7 · 63 · 6 · 7 · 4 · 2 · 5 · 8 · 9 · 17 · 3 · 1 · 6 · 4 · 2 · 9 · 5 · 84 · 2 · 6 · 5 · 9 · 8 · 7 · 1 · 39 · 8 · 5 · 1 · 7 · 3 · 4 · 6 · 2