Akari Puzzle Glossary — All Terms
Backtracking — Backtracking is an advanced solving technique — and the method computer solvers use when simple deduction is not enough. You pick an undecided cell, assume it holds a bulb, and propagate all consequences.
Choose an undecided cell and mentally assume "a bulb goes here." Propagate all consequences — illumination, neighbor counts, conflict zones. If you reach a contradiction (a numbered cell gets too many bulbs, or a white cell becomes impossible to illuminate), your assumption was wrong and that cell cannot hold a bulb. If no contradiction appears, continue until the puzzle is solved.
Experienced solvers tackling Hard puzzles on 12×12+ grids. Beginners should master constraint propagation and elimination first.
Choose an undecided cell near a cluster of numbered walls. This gives the most information per assumption.
Mentally place a bulb and propagate all consequences: illumination, neighbor counts, conflicts.
If any constraint is violated, your assumption was wrong — mark the cell with X. If no contradiction, the assumption may be correct.
If "bulb here" leads to no contradiction, try "no bulb here" and propagate. If that also leads to no contradiction, you need more information — pick a different cell.
No. Guessing means placing a bulb without logical justification. Backtracking is a systematic proof technique: you assume a position, derive all consequences, and check for contradictions. It is logically rigorous.
Only when constraint propagation and elimination are exhausted. On Easy and Medium puzzles, you should never need backtracking. On Hard 12×12+ grids, it may be necessary.
Yes. GridPaw's built-in solver uses constraint propagation as its first pass, then falls back to backtracking when simple deduction is insufficient.
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