Variant Sudoku

Simple Coloring

Link a digit’s spots through houses where it has only two, and paint them in two alternating colors. One color is all true, so a cell that sees both colors can’t be the digit.

Practice now
6
1
8
3
7
9
7
7
4
7
1
8
7
7
7
3
7
2
4
1
8
1
9
7
8
4
7
7
7
7
8
7
1
9
3
6
4
7
7
3
7
2
8
1
9
2
8
7
4
3
7
7
3
7
7
7
8
5
1
9
8
2
7
3
7
So it can’t be 7.

Why it works

On the board above:

Look only at the 7s. In a house with just two 7s, one of them is 7 and the other isn’t.

Join those pairs up and give them two colors. Blue: r6c1, r4c6 and r7c3. Orange: r6c4, r8c1 and r7c6.

One color is all 7s and the other has none. We don’t know which yet.

r8c3 sees a blue cell and an orange cell. Whichever color is right, it sees a 7. So it can’t be 7.

How to spot it

  1. Pick one digit

    Look only at its spots.

  2. Start at a house with two spots

    Paint one spot blue and the other orange.

  3. Follow the links

    From each painted cell, find other houses where the digit has two spots. Paint the partner the other color.

  4. Clear cells that see both colors

    Any unpainted cell that sees a blue and an orange spot loses the digit.

Practice

Real boards from the solver, with every pencil mark filled in. Spot it, then use it, then find it cold.

Loading the boards…

Try it in a real puzzle

Each of these needs a Simple Coloring to finish. It opens in the player.

Tips

Two of one color in a house

If two spots of the same color share a house, that color is false. All its cells lose the digit.

Use your color tool

Paint the notes in the player as you go. It is easier than holding it in your head.

ChainsA string of “if not this, then that” links. If both ends are the same digit, one of them must be it.Next: Chains →

In the glossary

Coloring