The 1-2-1 Pattern in Minesweeper
Most of the time you win at Minesweeper by counting one square at a time. But a handful of shapes show up so often that experienced players stop calculating and just recognise them. The most valuable of these is the 1-2-1 pattern — three numbers in a row that instantly tell you where two mines are and which cell is safe.
The pattern appears whenever you have a row (or column) of covered cells with the revealed numbers 1, 2, 1 running alongside them. It looks like it should be ambiguous. It isn't — the arithmetic only has one solution.
Reading the 1-2-1
- covered cell
- revealed number
- safe
- mine
Here's the logic, left to right. The left 1 touches the first two covered cells, so exactly one of them is a mine. The right 1 touches the last two covered cells — again one mine. The 2 in the middle touches all three covered cells and counts two mines among them.
Add it up. If the two outer cells were both safe, the middle 2 could never reach two mines. So both outer cells must be mines — which uses up the single mine each 1 is allowed. That forces the middle covered cell to be safe. Mines under the 1s, safe under the 2. Every single time.
The 1-2-2-1 sibling
The same family includes the 1-2-2-1, and it flips the result. Run the identical counting argument across four cells and the two middle covered cells (under the 2s) are the mines, while the cells under the 1s are safe.
A quick way to remember both: in a 1-2-1 the mines hug the ends; in a 1-2-2-1 they sit in the middle. Spot the shape, place your flags, and move on without doing the arithmetic again.
Where it shows up
These patterns are most common along the edges of the board and against walls of already-revealed cells, because that's where a number's neighbours get squeezed into a single line. Train your eye to scan for any 2 sitting between two 1s along a covered edge — it's almost always a free pair of flags and a safe click.
When the pattern lies
One caveat: the 1-2-1 shortcut only holds when the three numbers share the same line of covered cells and nothing else touches those cells. If another covered cell is hiding around a corner, the counts change and you're back to counting and subtraction. Check that the covered cells really are confined to one row before you trust the shape.
Play Minesweeper — three board sizes