Arrow · Medium

Locked Candidates in Arrow Sudoku

When a house can place a digit only where it meets another house, the digit is eliminated from the rest of that other house.

The idea

If every cell in a house that can take a digit also lies in a second house, the digit must go there, and the rest of the second house cannot have it.

On an Arrow board this works exactly as in Classic. The examples are from Arrow puzzles on this site.

Worked examples

A position from a real Arrow puzzle on this site. Step through it: the board lights what each step talks about, and the red lines show what rules what out.

A box and a line

Medium puzzle · Locked Candidates

In box 2, find every cell that can still take 8.

Step 1 of 4Step 2 of 4Step 3 of 4Step 4 of 4

Where it fits

MediumLocked Candidates is a Medium technique: Medium Arrow puzzles are the first to need it.

The Classic Locked Candidates lesson teaches it on a plain 9×9 board. The Arrow overview explains the rule and the levels.

Locked Candidates in the other styles: Sudoku X, Jigsaw, Thermo, Windoku, Kropki.

Try it on a Medium Arrow puzzle. Next Step points it out when it is the move.

The worked examples, every step

A box and a line

Medium Arrow puzzle · Locked Candidates

  1. In box 2, find every cell that can still take 8.
  2. All of them (R1C4, R3C4) are also in column 4. Box 2 must have an 8 somewhere in those cells, so the rest of column 4 cannot. The red lines point to the cells that lose 8.
  3. Eliminate 8 from R7C4, R8C4.
  4. Done: 8 is eliminated from R7C4, R8C4.

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