A
AiTechWorlds
AiTechWorlds
Watch a Sudoku solver try digits and backtrack cell by cell until the board is complete, with synced code.
def solve(g):
for r in range(9):
for c in range(9):
if g[r][c] == 0:
for v in range(1, 10):
if valid(g, r, c, v):
g[r][c] = v
if solve(g): return True
g[r][c] = 0 # backtrack
return False
return TrueA Sudoku solver fills each empty cell with a digit 1–9 that does not violate the row, column, or 3×3 box, backtracking whenever no digit fits.
| Time (worst) | O(9^m) |
| Space | O(1) |
The Sudoku Solver Visualizer animates how backtracking solves Sudoku: it finds an empty cell, tries digits 1–9 that don't violate the row, column, or 3×3 box, and backtracks when no digit fits. Worst-case time is exponential, but constraint checking prunes most branches. Watch each try and backtrack on the 9×9 grid.
Press Play
Watch the solver fill empty cells, trying digits and backtracking.
Step through
Use Step Forward/Back or the timeline to study each placement.
Read the code
View the Sudoku backtracking code in C++, Java, Python, or JavaScript and copy it.
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Last reviewed on June 14, 2026 by the AiTechWorlds Tools Team. All processing runs locally in your browser.