Strategy guide

Every Plankway puzzle can be solved without guessing. This guide shows how. It explains, with small example boards, each of the eight techniques that Plankway’s own solver uses to check every puzzle, in the order you will need them.

New to the game? Start with first steps. Already comfortable with the basics? Jump to the technique you get stuck on, or browse the puzzle archive, where every past daily is solved step by step with links back to this guide.

Getting started

• First steps: how to start a Plankway puzzle
  Where to begin on an empty Plankway board: the islands to look at first, how one bridge leads to the next, and a small puzzle solved step by step.
• Reefs: the Plankway twist on the bridges puzzle
  What reefs are in Plankway, how they block bridges, and how they change the counting: islands in line that cannot see each other, and fewer neighbours to share bridges.

Solving techniques

• Full island: when an island has all its bridges (weight 1)
  The most basic Plankway technique: once an island has as many bridges as its number, every other connection from it is ruled out.
• Every bridge counts: islands that need all they can get (weight 1)
  When an island’s number equals the most bridges its neighbours could give it, every possible bridge must be built. With examples for 4, 6 and reefs.
• Crossing bridges: one certain bridge blocks another (weight 1)
  Bridges may never cross. Once a bridge is certain, every connection that would cross it is ruled out, which often settles a neighbouring island.
• Bridge limits: when a double bridge does not fit (weight 1)
  An island cannot take more bridges than it still has room for. Why a 1 never gets a double bridge, and how to use the remaining room of an island.
• At least one: bridges you know exist before you know how many (weight 2)
  When the other neighbours of an island cannot supply enough bridges, some connections need at least one bridge. The key to 3s in corners and 5s with three neighbours.
• Avoid isolation: never close off a finished group (weight 3)
  All islands must form one network, so a bridge that would complete a group cut off from the rest is impossible. Why two 1s never connect, and two 2s never take a double bridge.
• The only way out: groups that must connect (weight 4)
  If a group of connected islands has just one possible connection left to the rest of the board, that bridge must exist. A key technique for Thursday to Sunday puzzles.
• Try and see: following an assumption to a contradiction (weight 6)
  The most advanced Plankway technique: assume a choice, follow the simple consequences, and if they lead to a contradiction, the opposite is true. Needed on some weekend puzzles.

Background

• Hashiwokakero: a short history of the bridges puzzle
  Where the bridges puzzle comes from: Hashiwokakero from the Japanese publisher Nikoli, its names around the world, what makes it a good logic puzzle, and how Plankway builds on it.
• How Plankway puzzles are made
  Behind the scenes of the Plankway generator: building an island network, adding reefs, proving there is exactly one solution, and rating difficulty by the techniques a human needs.
• The weekly difficulty: from easy Monday to expert Sunday
  How the Plankway daily gets harder through the week: grid size, number of islands and reefs, and which techniques each day needs, plus how endless mode ramps up.

How to read the diagrams

• Columns are lettered and rows numbered, so "the 3 in C2" is the island with a 3 in column C, row 2.
• A solid brown line is a bridge that is already there; a blue line is the bridge the step deduces.
• A red dashed line with a cross is a connection that is ruled out; a grey dashed line is still possible, or an assumption.
• A yellow island is the one the explanation is about; a red one ends up with the wrong number of bridges. Grey rocks are reefs.

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