Flood It
Fill the board from the top-left corner before the moves run out. Greedy play is a good baseline and provably not the answer.
Greed is a good baseline and not the answer
The obvious strategy is to take whichever colour captures the most cells this turn, and it works surprisingly well — well enough that the move limit here is set from what a greedy player achieves, plus a little slack. That means careless play loses and thoughtful play wins, which is the only setting where the limit does any work.
Greed is not optimal, though. Taking a smaller region now can open a much larger one next turn, and the best play often looks like a wasted move. Flood It is NP-hard in general, so there is no fast exact solver to compare against and none is offered here — the greedy button is a baseline to beat rather than a hint. More colours make it harder in a measurable way: six colours needs meaningfully more moves than four on the same size of board.
How to use
- Pick a colour; your top-left region takes it and absorbs touching cells.
- Fill the whole board before the move limit runs out.
- The number on each colour is what it would capture this turn.
- Biggest gain now is a good guess and often not the best move.
Frequently asked questions
How does Flood It work?
You control the region connected to the top-left corner. Each turn you choose a colour, that whole region becomes it, and any touching cells of the same colour are absorbed into the region. The aim is to swallow the entire board before your moves run out.
Is taking the biggest region always right?
No, though it is a strong baseline. Taking a smaller region now can open a much larger one next turn, so the best play sometimes looks like a wasted move. The greedy strategy is good enough that the move limit here is set from what it achieves, so beating the limit means beating greed at least occasionally.
How is the move limit chosen?
From the board itself rather than by taste. The game plays a greedy solution behind the scenes and sets the limit a little above the number of moves that took. That way a careless player loses and a thoughtful one wins, which is the only setting where a limit does any work at all.
Is there a perfect strategy?
Not a fast one. Flood It is NP-hard in general, so finding the shortest possible solution is computationally hard for large boards, which is why no exact solver is offered here. The greedy button is a baseline to compare yourself against rather than a hint at the right answer.
Do more colours make it harder?
Yes, measurably. A six-colour board takes noticeably more moves to fill than a four-colour board of the same size, because each turn captures a smaller share of what is adjacent. Fewer colours means bigger natural regions and faster spread.
Does board size or colour count matter more?
Colour count, generally. Doubling the board area increases the number of moves needed far less than adding colours does, because the region grows roughly geometrically while the board grows linearly in area. A large board with four colours is often easier than a small one with six.
Why does the region sometimes barely grow?
Because the colour you picked was not touching much of your region. The number shown on each colour button is exactly what it would capture this turn, so a low number means that colour is not adjacent to much — and a colour with a low number now can still be the right setup move.
What is a good general approach?
Look one move ahead rather than only at this turn. A useful habit is to check whether a smaller capture now puts you adjacent to a large block of a single colour, and to think about reaching the far corners early, since cells stranded in a corner cost a whole move each to collect at the end.
Can the board ever be impossible?
No. Any board can eventually be filled given enough moves, because each turn either grows the region or leaves it unchanged, and there is always some colour adjacent to it. The move limit is what makes it a game — without one, every board is a formality.
Is the starting corner special?
Only by convention. The rules would work identically from any starting cell, and some versions of the game let you start anywhere or move the origin. Starting in a corner makes the game slightly harder, because a corner region has fewer neighbours to grow into than a central one would.
Where did Flood It come from?
It appeared as a browser and mobile game around 2006 and spread quickly because the rules fit in a sentence. Mathematicians took an interest shortly afterwards, and the proof that finding an optimal solution is NP-hard was published a few years later.
Does the game save my progress?
No. Everything runs in your browser, nothing is stored or uploaded, and closing the tab loses the current board. Each new board is generated randomly, so you will not see the same one twice.
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