Daily logic puzzle
Masyu online, a new lake every midnight.
Masyu is a loop puzzle with two kinds of circle: the loop goes straight through a white one and turns just before or after it, and turns on a black one while going straight on both sides. Ours is called Swans, it is free, there is no account and no advertising, and a new one appears at midnight.
- a new lake at midnight, easy on Monday and ten by ten on Sunday
- exactly one solution, reachable by reasoning, checked by program
- hints that explain the technique, a two step Check, no red ink while you play
Today's lake. White swans are the straight ones, black swans the turns.
The rules
Three rules, and that is the whole game.
Masyu is sometimes published as White and Black Pearls. The rules are the same under either name.
- Draw one loop through every swan. The loop runs from the middle of one cell to the middle of the next, up and down or left and right, never diagonally, and it never crosses itself, branches, or passes through the same cell twice.
- A white swan means the loop goes straight through it and turns in the cell just before or just after. A black swan means the loop turns in that cell and goes straight through both neighbouring cells.
- Cells with no swan may be left out of the loop altogether. Exactly one loop fits every swan.
Our name for it
We call it Swans.
The puzzle is known as Masyu, which means evil influence in Japanese. We call ours Swans because the loop is the path a swan takes across the lake, and because white and black circles are easier to keep apart when they are two birds rather than two shades of the same dot.
The rules are untouched. The usual openings apply: a black circle on an edge is forced away from the edge, two black circles side by side force each other, and a row of three white circles fixes its own direction.
Where to start
Three ways in.
The archive of past lakes is free as well and goes back a year: Swans archive.
- Play today's lake
The daily puzzle, easy on Monday and ten by ten on Sunday, new at midnight.
- How to play Masyu
The rules with a worked example, the controls and the forced patterns worth learning.
- Practice sets
Sets by difficulty when one lake a day is not enough.
One solution
A program says so, not a person.
Every puzzle we publish has exactly one solution, and it is a program that decides. The generator throws a candidate away unless the solver returns exactly one solution and unless a second solver, restricted to human style reasoning, finishes it without guessing.
You can see the check yourself: the file tests.mjs in the game folder runs it over thirty days in every size. In Masyu that matters because the loop can satisfy every circle and still close early, leaving a separate loop elsewhere on the lake.
While you play, nothing goes red. A mistake is shown only by Check, in two steps: first how many segments are wrong and roughly where, then which ones. Hint works the same way, first the technique and the circle, then the move.
Questions
Questions about Masyu.
What is Masyu?
A loop puzzle on a grid with white and black circles. You draw a single closed loop through the centres of cells. At a white circle the loop passes straight through and must turn in at least one of the two neighbouring cells; at a black circle the loop turns, and goes straight through both cells it leaves into. Cells without circles may be skipped.
Is it free here?
Yes. The daily puzzle, the practice sets, the archive going back a year, the hints and the Check are all free, with no account and no advertising. We sell printable puzzle books on the same site, and that is the whole business model.
What is the difference between a white and a black circle?
A white circle is a straight, with a turn immediately before or after it. A black circle is a turn, with two straights leading away from it. Getting those two the wrong way round is the single most common mistake, which is why we draw them as two different birds rather than two dots.
Does the loop have to pass through every cell?
No. Only the circles have to be on the loop. Empty cells may be left out entirely, and in most puzzles a good number of them are.
Do I ever have to guess?
No, and that is checked rather than promised. Every published puzzle was solved by a program restricted to reasoning before it was allowed out. If you are stuck, Hint names the technique and the circle before it draws anything.
Where can I get more of these on paper?
In the Swans book: one hundred Masyu puzzles as a printable PDF in A4 and US Letter, with the solutions at the back. There is a free five puzzle sample to look at first. See the <a href="/puzzle-books/masyu-puzzle-book/">Masyu puzzle book</a>.
Related
More of the same.
One hundred of these on paper, with the solutions at the back: Masyu puzzle book (PDF, free sample).
All ten daily games are on one page: daily logic games.
Auf Deutsch: Masyu online spielen.