## Futoshiki game info

### Rules

- Fill the grid with numbers ranging from 1 to the size of the grid (e.g. 1 to 6 for a 6x6 puzzle).
- In each row and column, a number should appear exactly once.
- Numbers should honour the less-than (<) and greater-than (>) signs.

The digits on the board should form a Latin square when completed.

### Difficulties

There are three difficulties of Futoshiki puzzles in our implementation: Easy, Medium, and Hard.

The Easy puzzles are smaller and have more information that will help you solve the puzzle (starting numbers and inequality signs). The Medium and Hard puzzles are larger in size (up to 9x9). Hard puzzles have fewer starting numbers and fewer inequality signs than Medium puzzles.

### How to solve a Futoshiki puzzle?

Solving a Futoshiki puzzle requires logical reasoning. It is best to use pencil marks indicating the remaining possibilities for a cell. With logical reasoning, you can reduce the possibilities for a cell until there is only one possibility, or if a number is only possible for one cell in a row or column.

There are two types of information that can be used to solve the puzzle:

- A number cannot appear more than once in a row or column, so if you enter a number in a cell, you can remove it from the pencil marks of the other cells in the row and column.
- The inequality signs make certain possibilities impossible. Especially chains of inequality signs allow the removal of multiple pencil marks.

One useful pencil mark technique you can use is called *AB elimination*. If you have two cells in a row (or column) that both have two equal remaining possibilities, you can remove them from the other cells in that row (or column).

For example, if you have a row with four open cells, having possibilities {1,2} - {1,2} - {1,3,4} - {2,3}, you know that the 1 and 2 will go into the first two, so you can remove them from the possibilities of the other cells. The updated possibilities are: {1,2} - {1,2} - {3,4} - {3}.

### How to start a Futoshiki puzzle?

The best way to start a Futoshiki puzzle is to look at the inequality signs. Sometimes you can immediately fill in certain cells, e.g. if it is smaller than 2 (you know for sure it must be a 1).

Once these are filled in, you can press the *Add Pencil Marks* button to automatically generate all possibilities for the grid squares. Now you have to iteratively reduce the possibilities in the cells until there is only one left.

### Controls

You can either play with the mouse or with the keyboard.

Using the mouse, press a cell to select it, and select the number you want to fill in from the options above the grid.

With the keyboard, you can move around the grid using the arrow keys. If you want to fill in a number, just press the corresponding number key on your keyboard. There are some additional shortcuts:

- P: Add all pencil marks.
- E: Switch between entering numbers or entering pencil marks.
- Z: Undo a move.
- Y: Redo a move.
- R: Reset the current puzzle to its initial state.
- S: Save your progress for the current puzzle.
- ESC: Deselect a cell.
- BACKSPACE: Erase the contents of a cell.

### Similar games

Futoshiki is similar to other logic puzzles such as Sudoku, Numbrix, and Str8ts.

### System requirements

Futoshiki can be played in all modern browsers, on all device types (desktop, tablet, mobile), and on all operating systems (Windows, macOS, Linux, Android, iOS, ...).