Minesweeper 1-1-1-1 Pattern

Four 1s sit below four covered squares. Call the covered squares A, B, C and D from left to right. Both ends have mines. The two middle squares are safe.

See the pattern step by step

Four covered squares, A through D, sit above four 1s. The end clues each touch two covered squares. The inner clues each touch three. Subtract A + B = 1 from A + B + C = 1 to clear C. Compare B + C + D = 1 with C + D = 1 to clear B. Each end 1 then needs its outer square. Flags mark mines in the outer squares, A and D. Circles mark the inner squares, B and C, as safe. The four clues stay 1-1-1-1. — Download image

Board example

A + B = 1 and A + B + C = 1, so C is safe. B + C + D = 1 and C + D = 1, so B is safe.

Before

Four covered squares, A through D, sit above four 1s. The end clues each touch two covered squares. The inner clues each touch three.

After

Flags mark mines in the outer squares, A and D. Circles mark the inner squares, B and C, as safe. The four clues stay 1-1-1-1.

Why it works

Compare the first two 1s to clear C. Compare the last two 1s to clear B. The left end 1 now needs a mine in A. The right end 1 needs a mine in D.

Subtract A + B = 1 from A + B + C = 1 to clear C. Compare B + C + D = 1 with C + D = 1 to clear B. Each end 1 then needs its outer square.

The rule

The left 1 touches A and B. The next 1 also touches C. At the other end, the right 1 touches C and D. The 1 beside it also touches B.

What to check

The four squares above the row must be the only unknown neighbors of these clues. A longer row or an extra covered square changes the groups. Match the whole example before you use its result.

Try this board

Read the board, then choose

The left 1 touches A and B. The next 1 also touches C. At the other end, the right 1 touches C and D. The 1 beside it also touches B.

A two-row, four-column board has covered A through D above four 1s. The left end clue touches A and B, while its neighbor also touches C. Comparing them proves C safe. At the right end, compare C + D = 1 with B + C + D = 1 to prove B safe. The end clues then force mines in A and D. The top row remains covered in this drawing.

Choose a covered square. Then decide whether it is safe, has a mine, or needs more information.

Why this answer is correct

A: Mine · B: Safe · C: Safe · D: Mine

The shown covered squares are the only unknown squares around these numbers. Gaps stand for open squares or the board edge. Check every nearby square before you apply the result. Flags in these examples mark known mines.