Masyu

Masyu is a single-player logic puzzle originating in Japan.

Two kinds of symbols are placed onto a grid and the object is to draw a single continuous line through them following a few simple rules:* The loop must be a continuous path that begins and ends at the same point.

• The loop must not pass through a cell more than once.
• All segments of the loop must be horizontal or vertical lines.
• The loop must pass straight through a white circle cell, but make a 90° turn in the next and/or previous cell in the path.
• The loop must make a 90° turn on a black circle cell, but has to travel straight through the next and previous cells in the path.

Optional player aids consist of in-game instructions which open in a new window, a self-explanatory 'Prevent Illegal Moves' function, a 'Verify Puzzle' option which colours correct connections green and incorrect lines red, and an 'Undo Last Move' function.

This game has three difficulty levels, a save feature, a print function so the player can solve the puzzles without a computer, a pause key and a 'boss key' which instantly minimises the game but keeps it running.