1-2-2-1 pattern

Level: Advanced

A 1-2-2-1 along a wall confirms the two middle cells as mines.

1-2-2-1 is an extended pattern with four numbers placed in a row along the border. The mines the two 2s demand overlap, which determines the arrangement uniquely.

In a standard 1-2-2-1, the cells below the two middle 2s (outside the border) are confirmed as mines, and the cells below the end 1s are safe. It's an essential wall pattern that pairs with the 1-2-1.

Recognizing patterns like this along a long wall lets you confirm several cells at once, greatly speeding up your progress on advanced boards.

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