How to play Tents
A campsite seen from above, with trees dotted about. Pitch one tent beside every tree, directly above, below, left or right of it, so that the number beside each row and above each column counts its tents. Tents like their space: no two may touch, not even at a corner.
Boards come in three sizes, 6 × 6, 9 × 9 and 12 × 12, each generated in your browser with exactly one answer that you can reach without guessing. The small board is a coffee-break warm-up; the large one has 29 trees.
Rules
- Every tree gets one tent of its own, on a square that shares a side with it. A tent may stand beside other trees too, but it belongs to only one.
- So there are exactly as many tents as trees, and every tent stands beside a tree.
- No two tents touch, side by side or corner to corner.
- The number beside a row or above a column says how many tents it holds.
- Grass is your own note for squares without a tent, and the game ignores it when it checks the board. Touching tents, a tent with no tree beside it and a tree with no free side left turn red. A count turns red when its line has too many tents or no room for the rest, and fades once it is met.
- Click a count once its tents are in to grass over the rest of that line. Auto-grass dots every square that can no longer hold a tent; use it or not, your times count the same. Each size remembers its own board, and the clock pauses while the tab is hidden.
Controls
- Click / tap
- Cycle a square: empty → tent → grass → empty
- Right-click / long-press
- Toggle grass
- Drag
- Grass (or clear grass from) every square you pass over
- Click / tap a count
- Grass over the rest of a line whose tents are all in
- Arrows / WASD
- Move the keyboard cursor
- Space / Enter
- Cycle the square under the cursor
- T / G
- Toggle a tent / grass
- F
- Grass over the cursor’s row and column if their tents are in
- Backspace
- Clear the square
- O
- Toggle auto-grass
- Z / Ctrl+Z
- Undo
- P
- Pause
Tips
- Start with the zeros: a row or column marked 0 is all grass, and so is every square with no tree beside it.
- When a count equals the room left in its line, every open square takes a tent. Remember that tents in one line can’t stand side by side: a 2 with three open squares in a row takes both ends.
- A tree with a single free side has its tent there. Once a tent goes down, grass the eight squares around it.
- Drag across empty stretches to grass them in one stroke, and click a count the moment its tents are all in.
Tents strategy
Count the room, not the squares
Tents in one line can’t stand side by side, so a stretch of open squares holds at most half its length, rounded up. Compare each count with that room. A 2 with three open squares in a row takes both ends; a 3 whose open squares come as three separate pairs puts one tent in each pair, which already grasses the squares beside those pairs in the next lines.
Squares that touch every option
When a line’s last tent must go in one of two neighbouring squares, the two squares directly above them and the two directly below touch either choice, so they are grass. The same goes for a tree with two free sides meeting at a corner: the square diagonally between them touches both, so it can never hold a tent.
Pair trees with tents
Every tree needs a tent of its own. If a group of trees has, between them, exactly as many free sides as there are trees, every one of those squares is a tent. And a tent that is the only option for one tree is spoken for: a second tree beside it still needs its own tent somewhere else.
A short what-if on the big boards
On 9 × 9 and 12 × 12 the generator sometimes relies on a one-step test: put a tent on a square and follow the direct rules, grass round the tent, the counts and the trees with one side left. If a count overflows, a line runs out of room or a tree is left with nowhere to go, the square is grass. Undo back and mark it. Since each board has one solution, a contradiction is proof.
About Tents
The Dutchman Léon Balmaekers invented the puzzle, and it first appeared in 1989 in Breinbrekers, a Dutch puzzle magazine, under the name Alle ballen verzamelen, “collect all the balls”. In the Netherlands it is now called Tentje-boompje, and in Germany Zeltlager.
Here each board starts with tents scattered at random so that none touch, each given a tree on a free side, and the counts are read off that layout. A solver then works the board the way a person would: the counts, the ring round each tent, trees with one free side, and which trees can still pair with which tents. On the 9 × 9 and 12 × 12 it may also test a square, follow those rules and back out if something breaks. Only boards it finishes are kept, which proves the answer is unique, and every 12 × 12 needs at least one such test somewhere.
Questions
Can I always solve it without guessing?
Yes. Every board was solved by reasoning before you saw it. On the larger boards a step may take a short “what if”: put a tent on a square, follow what it forces, and if a count or a tree breaks, that square is grass.
Can a tent stand beside two trees?
Yes, but it counts for only one of them. Each tree needs its own tent, so there are always as many tents as trees.
Can tents touch trees, or trees touch each other?
Both are fine. Only tents may not touch other tents, corners included.
What does auto-grass do?
It dots every empty square that can’t hold a tent: one with no tree beside it, one next to a tent, or one in a row or column whose tents are all in. It is a display aid, and your times count either way.
Is my board saved if I leave?
Yes, in your browser, one board per size. The clock pauses while the tab is hidden.
