Unique Rectangle Type 5

Level 6 · Orange Belt (Green Stripe)

Strategy:

Unique Rectangles

Requires:

Unique Rectangle Type 1

Overview

Unique Rectangle Type 5 occurs when two diagonal cells of the rectangle share an extra candidate beyond the deadly pair. To avoid the deadly pattern, one of these diagonal cells must contain the extra candidate.

How It Works

Find a potential deadly rectangle with candidates {X,Y}.
Two diagonally opposite cells have the same extra candidate Z.
To prevent the deadly pattern, at least one diagonal cell must be Z.
Eliminate Z from cells that see both diagonal cells containing Z.

Example

Look for Unique Rectangle Type 5.

Sudoku grid showing the initial puzzle state for Look for Unique Rectangle Type 5.

1

Unique Rectangle Type 5

Find four cells forming a rectangle across 2 boxes. Two cells have only { 1, 7 }.

Sudoku grid illustrating step 1: Unique Rectangle Type 5 — Find four cells forming a rectangle across 2 boxes. Two cells have only { 1, 7 }.

2

Unique Rectangle Type 5

Extra candidate 4 appears in three UR cells: r1c5, r1c8 and r2c8.

Sudoku grid illustrating step 2: Unique Rectangle Type 5 — Extra candidate 4 appears in three UR cells: r1c5, r1c8 and r2c8.

3

Unique Rectangle Type 5

To avoid the deadly pattern, at least one of these cells must be 4.

Sudoku grid illustrating step 3: Unique Rectangle Type 5 — To avoid the deadly pattern, at least one of these cells must be 4.

4

Unique Rectangle Type 5

Eliminate 4 from cells seeing all three: r1c7.

Sudoku grid illustrating step 4: Unique Rectangle Type 5 — Eliminate 4 from cells seeing all three: r1c7.

5

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

Type 5 works with diagonal corners rather than same-side corners like Type 2.
The extra candidate Z appears in exactly two diagonally opposite cells.
A variant exists where Z appears in three of the four cells.