Twindoku

Two symbols. One answer. No guessing, ever.

Twindoku is a pure logic puzzle. Fill each square of the grid with a sun or a moon until the board satisfies every rule the level lists. Every rule in play is printed above the board, so nothing is hidden and nothing is left to luck.

ONE ANSWER, ALWAYS REACHABLE Each level has exactly one valid solution, and at any point in a solve there is at least one square you can prove from the rules in front of you. You never guess, and you never have to undo a wrong branch. The cells that come pre-filled are your starting foothold.

THE BASICS TAKE TWO TAPS Tap an empty square and a picker opens right where you tapped; choose a sun or a moon, tap again to switch.

• Balance: each row and column holds the same number of suns and moons -- 3 and 3 on a 6x6 grid, 4 and 4 on 8x8.
• No three in a row: never three of the same symbol side by side, across or down. Diagonals do not count.

THEN THE RULES START STACKING From level 3 on, every puzzle adds one or two more rules over the basics:

• Equal and cross markers: two neighboring cells that must match, or must be opposite.
• Color regions: each colored area needs its suns and moons balanced too.
• Blocked cells: cannot be filled, do not count for their row or column, and break up a run.
• Edge numbers: which cell holds the first sun of that row or column.
• Junction numbers: how many suns sit in the 2x2 block around the number. A 0 or a 4 decides four cells at once.
• Boards that are not square: diamonds, fat crosses, hearts, bow ties, octagons, window frames. Outside the outline is background -- untappable, uncounted.

HINTS THAT TEACH The hint tool finds a square that can be proven right now, highlights it, and explains the deduction -- which rule, and what on the board makes it certain. You read the reasoning, then press Apply. You keep the technique.

MISTAKES ARE NOT THE END Three hearts per level. A wrong symbol costs one heart and names the rule it broke. Out of hearts, revive to get them back with your last move undone, or restart the level clean. There is no dead end, so you can stay with a grid until it cracks.

GOOD FIT IF YOU LIKE Sudoku, Binairo, Takuzu, Binoxxo, binary puzzles, Nonogram, Kakuro, or any brain teaser you finish by reasoning instead of luck.

Fill every square, satisfy every rule, and the board solves itself.