Logic puzzle

Akari (Light Up), known in Japan as Bijutsukan (art gallery), is a logic puzzle where you place bulbs in white cells to illuminate the grid. Number clues on black cells constrain how many bulbs may sit beside them. Pure deductive logic—no guessing required.

Nurikabe uses an island-and-sea metaphor: numbered white islands must reach the correct size, separated by a single connected black sea. No 2×2 black blocks allowed. The name comes from a folklore creature—an invisible wall that blocks night travellers—a perfect fit for the puzzle's constraint.

Slitherlink (also Fences) is a loop puzzle on a dot grid. Numbers in cells tell you how many of that cell's four edges belong to the loop. Draw a single closed loop that satisfies every clue—deductive and visual.

Masyu (Pearl Necklace) is a loop puzzle with white and black pearl constraints. White pearls: straight through, turn in an adjacent cell. Black pearls: turn in the pearl, straight in both adjacent cells. Elegant and visual, with a famous naming mix-up.

Hashiwokakero (Bridges, Hashi) connects numbered islands with bridges. Each island must have as many bridge connections as its number. Bridges cannot cross; at most two between any pair. Graph-theory elegant.

Shikaku (Divide by Box) partitions the grid into rectangles. Each rectangle contains one number equal to its area. Factorisation determines shape options—prime clues force 1×n. Created by a Kyoto University maths student.

Hitori ("leave me alone") shades cells until each number is alone in its row and column. No two shaded cells touch; all unshaded cells form one connected region. NP-complete; the playful name is beloved in puzzle communities.

Kakuro (Cross Sums) uses a crossword grid with number sums instead of words. Digits 1–9, no repeats per block. Second only to Sudoku in Japan. Pure logic—arithmetic-free despite the sums.

Numberlink connects matching pairs with non-crossing paths. Fill every cell. Known digitally as Flow Free—one of the most downloaded puzzle apps ever. Spatial and intuitive.

Fillomino fills every cell so regions of orthogonally connected cells equal their number. Regions of equal size never touch. No region boundary is given—you infer it all.

Yajilin (Arrow Ring) combines arrow clues (counting black cells) with loop logic. Each clue counts black cells in a direction; draw a loop through all non-clue, non-black cells. Combines counting and loop constraints.