Lesson 6 of 7
Patterns
3 min

The 1-2-1 Pattern in Minesweeper

The 1-2-1 is one of the patterns players spot most often along the edge of an opened area. It settles five hidden cells at once, and it is nothing more than two 1-2s, read from each end.

Step 1 of 4

1 2 1
Row 4 reads 1, 2, 1 in columns 3 to 5, under a straight edge of five hidden cells. Read it from the left 1: the 2 puts a mine past itself, above the right 1. Read it from the right 1: the 2 puts a mine above the left 1. That is all the 2's mines, so the cell above the 2 is safe. In a 1-2-1, the mines are above the 1s. The two mines are starred.
Flag and open
Use the whole pattern: two flags and one safe cell.
Your move
Flag the 1-2-1's two mines, then open the cell above the 2.
A 1-2-1 in disguise
Row 4 reads 2, 2, 1 in columns 3 to 5. That's no 1-2-1, until you take the flag into account. The first 2 touches the flag in row 5, column 2, so it needs only one more mine: read it as a 1, and the row reads 1, 2, 1.
Your move
Find the 1-2-1 hiding here: flag its two mines and open the cell above its 2.
The ends of the pattern
The 1-2-1 is flagged now, and the cell above its 2 is open. What about the starred cells at either end, in row 3, columns 2 and 6?
Question

What you learned

Along a straight edge, 1 2 1 means mines above the two 1s and a safe cell above the 2.
The cells at both ends are safe too: the pattern settles five cells.
It is two 1-2s, one read from each end.
Take flags off a number first: a 2 next to a flag counts as a 1.