How to Master Flag a Mine
TLDR: Flag a Mine shows a partially-revealed Minesweeper board. Exactly one unrevealed cell is a guaranteed mine - provable by the numbers alone. Flag it by reading constraints, counting all eight neighbours precisely, and following forced conclusions. One wrong flag ends the run.
What You Are Training
Flag a Mine isolates the reasoning half of Minesweeper and removes the luck. Classical Minesweeper forces 50/50 guesses where no logic remains. Flag a Mine guarantees that at least one unrevealed cell is provably a mine based purely on the numbered hints around it - your job is to find it through constraint deduction alone.
The validator is bulletproof: a pure function called verifyGuaranteedMine enumerates every possible mine placement that satisfies all the revealed numbers. If your flagged cell contains a mine in every valid placement, you are correct. If even one valid placement leaves that cell empty, you are wrong. There is no preset flag to guess against. Pure constraint satisfaction is the only oracle.
Every puzzle is generated so at least one unrevealed cell is provably a mine. If you cannot find it, the answer is still there - it is a deduction you have not spotted yet, not a 50/50 guess you cannot solve.
How the Board Works
Revealed cells show either a number (how many of its eight neighbours contain mines) or a blank (zero adjacent mines). Unrevealed cells are face-down candidates.
Your task: identify which unrevealed cell must be a mine, based on the numbers, and flag it. One correct flag grows the streak by one. One wrong flag ends the run immediately.
Cells have king-adjacency: every cell touches up to eight neighbours - the four orthogonal cells and the four diagonal cells. A cell at the corner of the board has only three neighbours. A cell on an edge has five. A cell in the interior has eight. Counting adjacency incorrectly is the most common cause of wrong flags.
The Core Technique: Reading Number Constraints
Every number is a constraint. A cell showing “1” means exactly one of its neighbours is a mine. A cell showing “3” means exactly three of its neighbours are mines.
Start by scanning for numbers that have no remaining degrees of freedom:
- A cell showing “1” with exactly one unrevealed neighbour - that neighbour must be the mine.
- A cell showing “2” with exactly two unrevealed neighbours - both must be mines.
- A cell showing “3” with exactly three unrevealed neighbours - all three must be mines.
These are forced moves. No probability, no guessing - the mine count equals the unrevealed count, so every unrevealed neighbour is a mine.
Then scan in the opposite direction:
- A cell showing “0” has no adjacent mines - all its unrevealed neighbours are safe.
- A cell showing “3” where you have already identified three adjacent mines - all remaining unrevealed neighbours are safe.
Scan for extreme numbers first. A “0” forces all neighbours safe. A number equal to its total neighbour count forces all neighbours to be mines. These are your easiest and most confident forced moves - find them before analysing any ambiguous numbers.
The forced mine formula. For each revealed number N, count: flagged/confirmed mines around it (call this F), and unrevealed cells around it (call this U). If U equals N minus F, every unrevealed neighbour is a mine. If U is greater than N minus F, you cannot yet determine which specific unrevealed cells are mines - but you might after tracing other constraints.
Counting Neighbours Accurately
Do not estimate adjacency. For each number you analyse, trace its neighbourhood cell by cell. Count up, down, left, right, then the four diagonals. This is eight cells maximum, minus any that fall off the board edge.
For each neighbour, categorise it as: already-revealed (safe), confirmed mine, or unrevealed. The constraint is: confirmed mines + unrevealed mines = the number shown. If you have counted F confirmed mines already, the remaining mine budget is N minus F. If that remaining budget equals the unrevealed count, all unrevealed cells are mines.
Trace with your cursor: Move your mouse or finger around each number one neighbour at a time. Do not try to estimate by eye. Accurate counting prevents wrong flags on cells that look like mines but actually have a valid safe placement elsewhere.
Cascading Constraints
The power move in Flag a Mine is the cascade. When you confirm a cell as a mine, every number adjacent to that cell changes its constraint: the remaining mine budget for that number decreases by one. When you confirm a cell as safe, the unrevealed count for adjacent numbers decreases by one. Either update can force a new conclusion elsewhere on the board.
When stuck, update every affected number after each deduction:
- Mark an unrevealed cell as a mine (mentally or by flagging).
- For every number adjacent to that cell, reduce its mine budget by one.
- Check whether any of those numbers now have unrevealed count equal to remaining budget. If yes, those unrevealed cells are now forced mines.
- Repeat.
The safe-cell ripple. When you deduce that a cell is safe (not a mine), update every adjacent number’s unrevealed count. A “3” with four unrevealed neighbours (budget 3) becomes a “3” with three unrevealed neighbours (budget 3) - now all three are forced mines. Safe-cell deductions cascade into mine discoveries just as mine discoveries cascade into safe cells.
Common Mistakes
Flagging the first candidate you see. New players spot one unrevealed cell and flag it without verifying that it is forced. Always check: is there another unrevealed cell adjacent to the same number? If yes, the logic does not force this specific cell - it could be the other one. Keep analysing.
Misremembering adjacency at edges. A corner cell has only three neighbours, not eight. If you assume eight and count incorrectly, your forced-mine logic will produce wrong conclusions. Always count the actual neighbours, not the maximum possible.
Stopping after finding one forced conclusion. Many puzzles have only one obvious forced mine, but after cascading the update from that deduction, a second forced mine appears. Always propagate your deductions fully before picking your flag target.
If you have two candidates and neither seems forced: You have not finished the analysis. The puzzle is solvable - trace every constraint chain again. Often a safe-cell deduction from one number changes the constraint on an adjacent number and forces the mine elsewhere. Start fresh and count every neighbour explicitly.
When stuck, restart the scan. Return to the beginning of the board and check every number’s constraint from scratch. A deduction you made earlier may have changed what is possible elsewhere - constraints you dismissed as “not enough information yet” may now be forced. Fresh eyes on a partially updated board often spot the chain you missed.
Strategic Priority Order
For each new puzzle, work in this order:
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Find all zeros. A “0” instantly makes all its unrevealed neighbours safe. Mark them mentally. This is free information and often cascades.
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Find all saturated numbers. Any number where remaining budget equals unrevealed count - all those unrevealed neighbours are mines. Flag them.
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Propagate the updates. For every mine you confirmed and every safe cell you identified, update adjacent numbers. Check for new saturated numbers created by these updates.
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Narrow by elimination. If a number has three unrevealed neighbours but only needs one mine, and one of those neighbours is also adjacent to a number that forces it safe - that elimination might force which specific cell is the mine.
Building Your Streak
Rounds 1-5: Focus entirely on accuracy. If you are unsure, pause and recount all neighbours. A single wrong flag ends the run, so caution pays more than speed early on.
Rounds 6-10: Begin increasing pace. Forced moves from zeros and saturated numbers should now feel immediate. You are building pattern recognition for the most common constraint shapes.
Rounds 11+: Chase the streak. Push for confident flags within 20-30 seconds per puzzle. At this stage, constraint chains should feel instinctive rather than effortful.
After a wrong flag, before starting the next puzzle, identify which step broke down. Did you miscount a neighbour? Miss a cascade? Flag before confirming the mine was forced? Naming the error takes 10 seconds and prevents repeating it.
Consistency over length: A streak of 7 means you solved 7 consecutive puzzles with pure logic. Once you reach streaks of 5 consistently, you have internalised the constraint-reading skill. That skill transfers directly to classical Minesweeper - the deduction moves are identical, just faster to apply when the board is live.
Why This Transfers to Classical Minesweeper
Every constraint technique in Flag a Mine is a technique you use in classical Minesweeper. The difference is speed and context: in classical Minesweeper you are also clicking cells to reveal them, managing a full board, and occasionally hitting a 50/50 where no logic applies. The 50/50 guesses are pure luck. The 80% of moves before them - the forced mines and safe cells - are pure deduction.
Flag a Mine trains that deduction half in isolation. After 20-30 minutes of Flag a Mine, switch to classical Minesweeper and you will notice yourself flagging mines and clicking safe cells faster, with more confidence and fewer pauses. The bottleneck shifts from “can I reason this out?” to “how quickly can I execute what I already see?” That shift is mastery.
The transfer test. After a Flag a Mine session, open a classical Minesweeper board. Count how many forced moves you identify in the first 30 seconds. Before training: probably 1-2. After a month of Flag a Mine: likely 6-10. That number is your deduction speed, and Flag a Mine is what trains it.
Flag a Mine
Flag the unrevealed cell that must be a mine. Constraint-satisfaction deduction, cheat-proof validation
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