LITS, formerly known as Nuruomino (ヌルオミノ), is a binary determination puzzle published by Nikoli.

Rules

''LITS'' is played on a rectangular grid, typically 10×10; the grid is divided into

polyomino A polyomino is a plane geometric figure formed by joining one or more equal squares edge to edge. It is a polyform whose cells are squares. It may be regarded as a finite subset of the regular square tiling. Polyominoes have been used in pop ...

es, none of which have fewer than four cells. The goal is to shade in a

tetromino A tetromino is a geometric shape composed of four squares, connected orthogonally (i.e. at the edges and not the corners). Tetrominoes, like dominoes and pentominoes, are a particular type of polyomino. The corresponding polycube, called a tetracu ...

within each pre-printed polyomino in such a way that no two matching tetrominoes are orthogonally adjacent (with rotations and reflections counting as matching), and that the shaded cells form a valid

nurikabe The ''nurikabe'' (塗り壁 or 塗壁) is a ''yōkai'', or spirit, from Japanese folklore. Its name translates to "plaster wall", and it is said to manifest as an invisible wall that impedes or misdirects travelers walking at night. Sometimes re ...

: they are all orthogonally contiguous (form a single polyomino) and contain no 2×2 square tetrominoes as subsets.

History

The puzzle was first printed in ''

Puzzle Communication Nikoli A puzzle is a game, problem, or toy that tests a person's ingenuity or knowledge. In a puzzle, the solver is expected to put pieces together ( or take them apart) in a logical way, in order to arrive at the correct or fun solution of the puzzle ...

#106''; the original title is a combination of 'nuru' (

Japanese Japanese may refer to: * Something from or related to Japan, an island country in East Asia * Japanese language, spoken mainly in Japan * Japanese people, the ethnic group that identifies with Japan through ancestry or culture ** Japanese diaspor ...

: "to paint") and 'omino' (

). In issue #112, the title was changed to the present one, which represents the four (of five) tetrominoes used in the puzzle: the L-shape, the straight, the T-shape, and the skew (square tetrominoes may never appear in the puzzle as they are a direct violation of the rule).

Solving Strategies

There are some simple, and difficult, strategies for this puzzle.

Instantly solvable/Chains

There are 4 different "instantly solvable" cases, the L, S, T, and I can all be instantly solved in boxes that only have 4 blocks. There are also "chains" or 4 blocks eliminating a block from a 5 block box, creating another location for the next tetromino.

Inherent locational placements

If you see 5 pieces, you will always be able to place at least one block inside of the pentomino(like tetromino, but for 5). Like if you see a t with an extra block on the top, the two spots in the middle can be filled in, since every possible tetromino takes place in those 2 blocks. Every other location can be inherently assumed based on the amount of possible tetrominoes, and the overlapping tiles of all of them.

External links