Z80 Sudoku — Solver Control Structure

Deterministic Phase

1. Scan board for UNKN cells.2. Build candidate mask.3. If single candidate → fill cell.4. Repeat until no progress flag set.

Transition to Backtracking

If unresolved cells remain:• Select cell with minimum candidate count.• Push frame with remaining candidates.• Attempt candidates depth-first.

Backtracking Logic

• On failure, pop frame.• Restore previous state.• Try next candidate.• Continue until solved or stack empty.