Unique Rectangle Type 2

Level 6 · Orange Belt (Green Stripe)

Strategy:

Unique Rectangles

Requires:

Unique Rectangle Type 1

Overview

Unique Rectangle Type 2 is similar to Type 1, but two cells (on the same side) share an additional candidate. That extra candidate must be placed in one of them, so it can be eliminated elsewhere.

How It Works

  1. Find a potential deadly pattern rectangle with candidates {X,Y}.
  2. Two cells on the same side have one additional candidate Z (same in both).
  3. Z must be placed in one of these cells to avoid the deadly pattern.
  4. Eliminate Z from cells that see both of these "roof" cells.

Example

Look for Unique Rectangle Type 2.

1

Unique Rectangle Type 2

Find four cells forming a rectangle across 2 boxes. Two cells have only { 1, 9 }.

2

Unique Rectangle Type 2

The other two cells (r3c4 and r3c5) have { 1, 9 } plus extra candidate 7.

3

Unique Rectangle Type 2

To prevent a deadly pattern, one of these cells must be 7 (not 1 or 9).

4

Unique Rectangle Type 2

Any cell that sees both roof cells would then see that forced 7, so those highlighted cells cannot keep 7.

5

Unique Rectangle Type 2

Remove 7 from cells seeing both r3c4 and r3c5: r2c4, r2c6 and r3c7.

6

Result after applying the technique.

Tips & Patterns

  • The two cells with extra candidates must be in the same row or column (not diagonal).
  • The extra candidate Z is the same in both cells.
  • Type 2 makes eliminations outside the rectangle.