S.P.A.R.K. Edition — AI Tools
Sudoku Generator
Watch recursive backtracking build a valid puzzle from scratch — step by step
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200ms
Choose a difficulty and click Generate
Phase 1: Fill
Backtrack
Kept (needed)
Final given
Phase 1 — Fill:
Phase 2 — Remove: Each removed cell is verified by
fillGrid() recurses on each empty cell,
trying digits in random order. A red flash = backtrack (that digit failed downstream).
The depth in the log shows how deep the call stack is.
Phase 2 — Remove: Each removed cell is verified by
countSolutions()
(a second recursive function). A yellow flash = cell restored (its removal broke uniqueness).
Generator Log