Classic Sudoku · 23
Classic Sudoku · 23: 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: R1C7 = 7
After the preceding deductions, row 1, column 7 has only candidate 7. Its row, column and box exclude every other digit. Enter 7, then update the remaining candidates; this conclusion does not require consulting the completed answer.
Check the existing digits: row 1: 2, 3, 8; column 7: 4, 5, 8, 9; box: 1, 3, 5, 6, 8. Each digit already present rules out that candidate in this cell.
Deduction 2: R1C9 = 4
After the preceding deductions, row 1, column 9 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 1: 2, 3, 7, 8; column 9: 1, 6, 7, 8, 9; box: 1, 3, 5, 6, 7, 8. Each digit already present rules out that candidate in this cell.
Deduction 3: R2C7 = 2
After the preceding deductions, row 2, column 7 has only candidate 2. Its row, column and box exclude every other digit. Enter 2, then update the remaining candidates; this conclusion does not require consulting the completed answer.
Check the existing digits: row 2: 1, 6, 7; column 7: 4, 5, 7, 8, 9; box: 1, 3, 4, 5, 6, 7, 8. Each digit already present rules out that candidate in this cell.
Deduction 4: R2C8 = 9
After the preceding deductions, row 2, column 8 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 2: 1, 2, 6, 7; column 8: 2, 3, 8; box: 1, 2, 3, 4, 5, 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 1, column 7. From the starting grid, its legal candidates are 7. 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 · 1 · 2 · 9 · 6 · 7 · 3 · 43 · 7 · 4 · 5 · 8 · 1 · 2 · 9 · 69 · 2 · 6 · 7 · 3 · 4 · 5 · 8 · 16 · 8 · 2 · 9 · 4 · 7 · 3 · 1 · 54 · 9 · 7 · 3 · 1 · 5 · 8 · 6 · 21 · 3 · 5 · 8 · 6 · 2 · 9 · 4 · 77 · 6 · 9 · 4 · 5 · 3 · 1 · 2 · 82 · 1 · 8 · 6 · 7 · 9 · 4 · 5 · 35 · 4 · 3 · 1 · 2 · 8 · 6 · 7 · 9