Yin-Yang Logic Puzzle

Yin-Yang is a logic puzzle about splitting a square grid into one black group and one white group. Some cells start with a stone. You fill the rest. You can play grids from 6×6 up to 10×10, and every puzzle here has exactly one colouring that you can reach by logic, with no guessing. People also look this up as a yin yang puzzle, a yin yang logic puzzle, or a printable yin yang puzzle.

Rules

The board is an n×n grid. There are no numbers outside it. A filled circle is black. An outlined circle is white. A stone that is already on the grid is given, and it stays that colour.

Every cell is black or white. All of the black cells join along their sides, and all of the white cells join along their sides. Cells that touch only at a corner are not joined. No 2×2 block is a single colour.

An empty cell is not white. You have to place a stone in every cell. The puzzle is solved when that colouring is the one solution and both groups still hold.

Controls

Choose Black or White under the board. Tap a cell, or drag across cells, to place that colour. Tap a cell that already has the colour to clear it. A cell that has the other colour takes the new one. A drag follows the first cell: it places the colour, or it clears when that cell already has it. A given stone does not change. With a mouse, right-click places the other colour, or clears it when that colour is already there.

On a keyboard, the arrow keys move around the grid. Space or Enter places the selected colour, or clears it when the cell already has that colour. B or 1 places black. W or 2 places white. M switches Black and White. Backspace, Delete, or 0 clears the cell.

A cell turns red when a finished 2×2 is one colour or a checker, or when a colour is split into two groups or sealed away from the rest of its colour. Those marks appear only once the break is already forced. Press Hint for one step the rules already force, with a sentence saying why. Press Check when you want the board checked against the rules. An unfinished board, with any cell still empty, is not done. Undo and Redo step through your moves, and Reset clears the stones you placed. The given stones come back. When every cell matches the one colouring, the board turns teal.

Techniques

Easy grids follow from one small patch of the board:

• Avoid 2×2: three cells of a 2×2 are the same colour, so the last cell is the other colour.
• Avoid a checker: two diagonals cannot both be the opposite colour, so this cell matches the pair.
• Border arc: both colours already meet the border, so the cells between those two stones are the same colour.

Medium grids also look for a group with only one empty way out, when the same colour still sits outside it. Hard grids notice a cell that can no longer touch the rest of one colour, and they try the other colour in a cell when that choice would cut a group off or make a 2×2 block.

Beginner tips

Start from the stones that are already on the grid. If three cells of a 2×2 are the same colour, the fourth cell is the other colour.

When a colour has only one empty neighbour and the same colour sits outside that gap, the gap has to be that colour too. Filling it the other way would seal the group off.

If you are new to Yin-Yang, start with the daily 6×6 easy grid, or another 6×6 easy grid, and move up once the two groups and the 2×2 rule feel natural.