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Platon Sudoku · Sudoku Study

BUG + 1 · Step-by-step example

In BUG + 1, exactly one unsolved cell has three candidates and every other unsolved cell has two; the extra candidate occurs three times in its row, column, and box. Place the candidate that occurs three times in all three regions.

This course is adapted from Platon Sudoku App. Read the complete example here, then continue learning and practising in the app.

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Recognize the pattern

In BUG + 1, exactly one unsolved cell has three candidates and every other unsolved cell has two; the extra candidate occurs three times in its row, column, and box.

How to find it

Confirm every other unsolved cell is bivalue, then count the pivot’s candidates in each of its three regions.

What it allows

Place the candidate that occurs three times in all three regions.

Avoid the mix-up

One three-candidate cell is not enough by itself. The entire remaining grid must have the BUG+1 structure.

Step-by-step example · BUG+1

This example starts from a saved intermediate position. Its candidates include earlier logical eliminations; they are not fresh automatic notes.

Blue: evidence. Green: conclusion. Crossed-out digits: eliminated candidates. R1C1 means row 1, column 1.

Step 1 · Recognize the BUG + 1 state

Every other unsolved cell has exactly two candidates. R5C8 alone has three (5, 7, 9), so R5C8=9 is the one extra candidate beyond a BUG pattern. First verify its counts in the row, column, and box.

Every other unsolved cell has exactly two candidates. R5C8 alone has three (5, 7, 9), so R5C8=9 is the one extra candidate beyond a BUG pattern. First verify its counts in the row, column, and box.
Every other unsolved cell has exactly two candidates. R5C8 alone has three (5, 7, 9), so R5C8=9 is the one extra candidate beyond a BUG pattern. First verify its counts in the row, column, and box.
Step 2 · Count 9 in row 5

In row 5, 9 occurs at R5C1, R5C7, R5C8: 3 positions.

In row 5, 9 occurs at R5C1, R5C7, R5C8: 3 positions.
In row 5, 9 occurs at R5C1, R5C7, R5C8: 3 positions.
Step 3 · Count 9 in column 8

In column 8, 9 occurs at R4C8, R5C8, R9C8: 3 positions.

In column 8, 9 occurs at R4C8, R5C8, R9C8: 3 positions.
In column 8, 9 occurs at R4C8, R5C8, R9C8: 3 positions.
Step 4 · Count 9 in box 6

In box 6, 9 occurs at R4C8, R5C7, R5C8: 3 positions.

In box 6, 9 occurs at R4C8, R5C7, R5C8: 3 positions.
In box 6, 9 occurs at R4C8, R5C7, R5C8: 3 positions.
Step 5 · The one extra candidate must be true

The counts show R5C8=9 is the only extra occurrence. Removing it would leave every unsolved cell bivalue and every missing digit occurring twice in each region—the ambiguous BUG state. Because this puzzle has one solution, R5C8=9 must be true.

The counts show R5C8=9 is the only extra occurrence. Removing it would leave every unsolved cell bivalue and every missing digit occurring twice in each region—the ambiguous BUG state. Because this puzzle has one solution, R5C8=9 must be true.
The counts show R5C8=9 is the only extra occurrence. Removing it would leave every unsolved cell bivalue and every missing digit occurring twice in each region—the ambiguous BUG state. Because this puzzle has one solution, R5C8=9 must be true.

What it allows

The counts show R5C8=9 is the only extra occurrence. Removing it would leave every unsolved cell bivalue and every missing digit occurring twice in each region—the ambiguous BUG state. Because this puzzle has one solution, R5C8=9 must be true.

BUG + 1 · Place the candidate that occurs three times in all three regions.
BUG + 1 · Place the candidate that occurs three times in all three regions.

Practice

This course is adapted from Platon Sudoku App. Read the complete example here, then continue learning and practising in the app.

View on Google Play