In the game LITS, the goal is to set some cells black and the rest white in order to satisfy the goals of the game (see Rules tab). To play, you can click on a cell to switch states, or use the arrow and other keys:

• A left-click turns a cell dark, a right-click turns it white, and a middle-click returns it to indeterminate (gray).
• Once the mouse is pressed down, you can drag the mouse to set multiple squares in one sequence.
• Alternately, you can use the arrow keys to move around the board, then press the space bar to toggle between the states, or the '1' key to turn black, the '0' key to turn white, or the backspace key to set back to indeterminate.
• Once on a cell, you can drag its color by holding the shift key and moving the arrow keys up down left or right.

In Assist Mode (0), the default, only the existance of errors or incomplete rooms is indicated. In Assist Mode (1), the number of errors and incomplete rooms is indicated, see game rules. In Assist Mode (2), errors are highlighted with different colors (red for violating the 2x2 rule (see Rules Tab), yellow for an incorrect shape), and completed LITS shapes are highlighted with green colors. In some cases the solve difficulty will greatly decrease in Assist Mode (2), so select depending upon the level of challenge desired. The canvas border will turn green if the grid is completed without error. You can press the "undo" button on the bottom of the page to undo previous moves.

Below, enter puzzle code (0-0) for one of a list of pre-defined puzzles, or a puzzle descriptor (see "Puzzles" tab). Puzzle code 0 shows an example completed puzzle that can be helpful. The following puzzle codes have demos, which will walk you through a solve to help you on the path to mastery: []).

LITS is a Japanese logic puzzle published by Nikoli. In LITS, the puzzle board begins with a collection of "polyominos", or collections of blank cells forming a room of various sizes and shapes. The player must set some of the cells dark, and the rest white, forming only the four-cell shapes 'L', 'I', 'T', or 'S', in any orientation. The rules relate these shapes and their arrangement on the solution board.

1. A room can only have four cells within it turned dark, and the remainder must be white.
2. The arrangement of the dark squares must resemble the letters 'L', 'I', 'T' or 'S'. See the completed solution using puzzle entry number 0 for an example.
3. Identical shapes (two 'L' shapes, for instance) can not touch vertically or horizontally, no matter their orientation. Diagonally touching is acceptable.
4. No 2x2 square of cells can be entirely shaded dark.
5. The dark cells must all form one contiguous "river" of cells, connected to each other in the vertical or horizontal direction. A river is not considered connected if it only flows through diagonally adjacent dark cells.

Below select puzzle 0 to see a completed sample grid. See the Game Play or Puzzles tab for how to invoke a demo.

Puzzles can be invoked by either a numerical entry from 0-0, or through a character description of the puzzle itself, entered into the Display form on the 'Game Play' tab. The numbered puzzles are hand-crafted of varying difficulty, roughly easy to hard. Puzzle 0 shows a completed correct puzzle.

To describe a puzzle, the character string must be of the form: "WxH::<wall-descriptor-rows:<wall-descriptor-columns>", where W is a number indicating the width of the grid, and H the height. The wall descriptors are a description of the true/false nature of the walls for each row, and then each column. These are denoted in hexadecimal value, which is a value from 0 to 15 denoted as 0-9,a-f for each collection of 4 walls, ignoring the sides. As an example, if a grid is 8 columns wide, then 7 wall values are needed to define the walls between column 0 and 1, then 1 and 2, etc. These 7 values are described in two-character hex values from 00 to fe. Extra unused bits for the end of a row or column are ignored, and each new row or column begins with a new hex pair or triplet. So if the top row has a wall between columns 0 and 1, and between columns 5 and 6, that would be binary value of 1000010, which is represented as the hex pair of 84. An example descriptor is as follows for entry 1: 'descr'.

For LITS there are 1 demo puzzles that can be helpful to walk through solving methods. They are puzzle codes []. Enter them in the Game Play tab with the code number and there will be added a demo panel to help with the solve.

This playground was written using javascript and is available open source. All code is checked into the github repo at ohmec/puzzles. Feel free to file bugs there!