Classic Sudoku · 04
Classic Sudoku · 04: 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: R4C9 = 9
After the preceding deductions, row 4, column 9 has only candidate 9. Its row, column and box exclude every other digit. Enter 9, then update the remaining candidates; this conclusion does not require consulting the completed answer.
Check the existing digits: row 4: 1, 2, 7; column 9: 4, 5, 6, 8; box: 1, 3, 4, 5, 7. Each digit already present rules out that candidate in this cell.
Deduction 2: R4C3 = 8
After the preceding deductions, row 4, column 3 has only candidate 8. Its row, column and box exclude every other digit. Enter 8, then update the remaining candidates; this conclusion does not require consulting the completed answer.
Check the existing digits: row 4: 1, 2, 7, 9; column 3: 3, 4, 5, 7; box: 2, 6, 7. Each digit already present rules out that candidate in this cell.
Deduction 3: R4C8 = 6
After the preceding deductions, row 4, column 8 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 4: 1, 2, 7, 8, 9; column 8: 2, 3, 4, 5, 7; box: 1, 3, 4, 5, 7, 9. Each digit already present rules out that candidate in this cell.
Deduction 4: R5C2 = 9
After the preceding deductions, row 5, column 2 has only candidate 9. Its row, column and box exclude every other digit. Enter 9, then update the remaining candidates; this conclusion does not require consulting the completed answer.
Check the existing digits: row 5: 1, 2, 3, 4, 5, 6, 7; column 2: 1, 2, 3, 5, 7; box: 2, 6, 7, 8. 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 4, column 9. From the starting grid, its legal candidates are 9. 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
8 · 5 · 4 · 9 · 1 · 6 · 2 · 7 · 31 · 6 · 9 · 2 · 7 · 3 · 4 · 8 · 57 · 3 · 2 · 4 · 8 · 5 · 9 · 1 · 63 · 2 · 8 · 1 · 5 · 4 · 7 · 6 · 96 · 9 · 7 · 8 · 3 · 2 · 1 · 5 · 45 · 4 · 1 · 7 · 6 · 9 · 8 · 3 · 22 · 8 · 5 · 6 · 4 · 1 · 3 · 9 · 74 · 1 · 6 · 3 · 9 · 7 · 5 · 2 · 89 · 7 · 3 · 5 · 2 · 8 · 6 · 4 · 1