Tendo: One Path

One puzzle a day. One line through it.

Draw a single unbroken line that touches every dot exactly once. Don't lift your finger. Don't visit a dot twice.

There is exactly one way through. Not one intended way — one. Every board is checked before it reaches you, and the day it cannot be checked is a day you don't get a puzzle.

THE WEEK HAS A SHAPE Monday is eight dots and takes a minute. Sunday is fifteen and does not. The board grows across the week, so the puzzle you meet on a Tuesday morning and the one waiting on Sunday are different kinds of afternoon.

Each week is named for something the boards do that week — bridges, crossings, dead ends, symmetry. The name is a line about the shape of the thing, not a lesson about it.

WHAT'S HERE · A new puzzle every day at 00:00 UTC · Exactly one solution, every day · Practice boards once you've finished the day's · Your solve time against everyone else's · English, 日本語, 繁體中文, 简体中文 · Works with no connection · No account, no sign-in, no email

WHERE IT COMES FROM The puzzle is William Rowan Hamilton's. He devised it in 1857 and sold it to the London games maker John Jaques for £25; it reached shops in 1859 as the Icosian Game, a wooden board with pegs and a piece of string. The board is long gone. The question it asked — can you visit every point exactly once, and how would you know — is still open in the general case, and is one of the questions modern computing is built on top of.

Tendo is that question, once a day, small enough to hold.