What are the rules of Slitherlink?
Slitherlink is a grid of dots with numbers in some of the squares between them. Draw one closed loop along the lines between the dots. The loop never crosses or touches itself, and a number says how many of that square's four sides the loop uses. Squares without a number can have any count, including none.
Choose a 5 × 5, 7 × 7 or 9 × 9 grid (5 × 5 is picked to begin with). Tap anywhere in a square near one of its sides to draw that side; tap again for a cross, your note that the loop doesn't go there, and again to clear it. Dragging draws along every side you pass. On a keyboard, the arrows move between squares and W, A, S and D mark the top, left, bottom and right side.
How do you solve Slitherlink?
- Cross out around every 0. None of its sides is used, which often starts a corner.
- Fill or cross when a number is settled. Once a 2 has two lines, its other sides are crossed; once a 3 has one cross, its other three sides are lines.
- Count at each dot. The loop enters and leaves a dot once or not at all, so a dot with two lines crosses out its others, and a dot with one line and one open side must use it.
- Don't close a loop too soon. A side that would close a small loop while lines remain elsewhere is crossed out, since there is only one loop.
How is your Slitherlink time calculated?
Your result is the time from Start until the lines make one loop and every number is right; crosses are only notes. Beside it are the times you used Check, which marks any line or cross in the wrong place, and Hint, which fixes a wrong mark or draws one side of the loop. There is no rating, because no published typical time exists for puzzles built like these.
Does every Slitherlink here have exactly one answer?
Yes. The 90 puzzles here were made ahead of time. Each loop is the outline of a random patch of squares; every square gets its count, then counts are taken away one at a time while a solver using the moves above can still finish without guessing. A separate search counts the loops that fit the numbers left. The site's tests count every stored puzzle again: exactly one loop each time.
Where does Slitherlink come from?
Slitherlink first appeared in June 1989 in issue 26 of Puzzle Communication Nikoli, the magazine of the Japanese publisher Nikoli. It is one of the puzzles where you draw the answer rather than write it, like Number Link, where paths join pairs of numbers, and Bridges, where lines join islands.