To play, click on a cell to toggle from light to dark. Alternately, you can use the arrow keys to move around the board, and press the space bar to toggle, or the '1' key to turn black, or the '0' key to turn white.

In Assist Mode (0), the default, only the existance of errors is indicated. In Assist Mode (1), the number of errors is indicated, be they duplicate digits per row or column, adjacent blackened cells, or stranded "rivers" of white cells. In Assist Mode (2), these errors are highlighted with 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 click 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). The following puzzle codes have demos, which will walk you through a solve to help you on the path to mastery: []).

Hitori (ひとりしてくれ Hitori ni shite kure; literally "leave me alone") is a Japanese logic puzzle published by Nikoli. The rules for Hitori are listed here.

1. No single digit can exist "enabled" in a single row or column. In this player, disabled cells are turned black.
2. There can be no two disabled cells adjacent to another horizontally or vertically (diagonally adjacent is OK).
3. The enabled (white) 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 white 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:<descriptor>", where W is a number indicating the width of the grid, and H the height. The descriptor is a definition of the grid contents from left to right, then top to bottom. A dot '.' can be used as a visual separator, for example between rows. Cell contents for values greater than '9' should use capital 'A' to 'Z' for 10 through 35. An example descriptor is as follows for entry 1: 'descr'.

For Hitori 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!