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Lizely

Fill One Line Puzzle

Trace one original continuous path through every open cell across five independently verified grids with pointer, touch, and keyboard controls.

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How to use

  1. 1.Begin at the numbered start cell, then click an orthogonally adjacent open cell or hold and drag across several adjacent cells.
  2. 2.Continue the single path without crossing a blocked square or visiting any open square more than once; use Undo or Reset level when needed.
  3. 3.Cover every open cell, choose Check path or press Enter, and clear all five fixed grids to earn exactly 1,000 points.

About Fill One Line Puzzle

Fill One Line Puzzle is a five-level spatial logic game about planning one continuous route through a grid. Every level begins at a numbered square. Your job is to extend the line through every open square exactly once. Moves are orthogonal, so the next square must be immediately above, below, left, or right of the current endpoint. Diagonal jumps are not allowed. Dark blocked squares are walls and can never be entered.

The challenge is easy to understand but cannot be solved by simply clicking a finish button. Every choice changes which cells remain reachable. A move that looks harmless can isolate a corner or divide the remaining open area into separate regions. Because visited cells cannot be used again, the order of moves matters. You must trace the actual route yourself; the game does not reveal the next square, complete the remaining route, or replace your choices with an automatic solution.

All five boards are original fixed puzzles. They use small grids, distinct obstacle arrangements, and fixed starting cells so each attempt is reproducible. The first level is an open three-by-three introduction. Later levels add a missing cell, protected corners, narrower corridors, and longer routes. An independent depth-first search oracle enumerates legal orthogonal paths for each literal board and confirms that its declared route visits every open cell exactly once. This provides a stronger check than merely running the same production validator twice.

To draw with a pointer, click an adjacent square or press and hold while moving across the grid. Real pointer dragging adds each square as the pointer enters it, provided that the square is open, unused, and next to the current endpoint. Touch input uses the same local interaction model. Each chosen square displays its step number, while the latest endpoint uses the accent treatment. The path-length counter shows how many open cells have been covered.

Keyboard play mirrors the grid rules. The arrow keys attempt to extend the route one cell from its current endpoint. An arrow that would leave the board, enter a blocked square, or revisit a used square has no effect. Delete or Backspace removes the latest step without removing the fixed start. Press X to reset only the current level, Enter to check the current path, and R to restart the complete five-level run. Buttons use native controls and maintain touch targets of at least 44 pixels.

Checking is deliberate. A level clears only when the path contains every open square. Clearing a level awards exactly 200 points and immediately prepares the fixed start of the next level. Five cleared levels therefore produce exactly 1,000 points. Checking an incomplete route records its exact level-and-path signature. Rechecking the identical unchanged route does not add another error. You may extend, undo, or reset after the first distinct incomplete check. A second different incomplete check deadlocks the run and requires Restart.

That two-check rule rewards inspection instead of rapid guessing. Before checking, look for unvisited corners and cells with very few available neighbors. A non-start corner often needs to be approached at the right moment because leaving it may be impossible. Obstacles can create bottlenecks, so consider which side of a narrow passage should be completed first. If a move strands a square, Undo returns one step at a time; Reset level returns to the fixed starting square without erasing the points earned on earlier levels.

Selection rules are atomic and predictable. Clicking the current cell, an already visited cell, a blocked cell, a nonadjacent cell, or a coordinate outside the board does nothing. Those invalid selections do not change the path or count as checks. Completion and deadlock are terminal states: movement, selection, undo, reset-level, and check commands no longer alter the game. Restart creates a fresh run with level one, zero points, no recorded checks, and the original starting path.

This is a cell-coverage puzzle, not an edge-tracing puzzle. In an Euler-style one-line drawing, a vertex may be visited more than once as long as each required edge is used correctly. Here, the open grid cells are the things that must be covered, and every open cell may appear only once. The distinction is visible in the numbered path and is enforced for pointer, touch, and keyboard input.

The game runs entirely in the browser. It does not upload a board, request an account, call an external API, or use a paid service. The best completed score is stored locally when browser storage is available. The shared game shell also supplies Restart and a double-Escape boss key that temporarily replaces the board with a spreadsheet-style cover. Press Escape twice again to return to the game.

No external factual dataset is embedded in the levels. The grid dimensions, blocked-cell positions, starting points, valid routes, scoring, copy, and mistake policy are product-authored. The depth-first search is used only to verify internal solvability; it does not claim that these boards come from a published puzzle collection. Fill One Line Puzzle is recreational practice in route planning and constraint awareness, not an intelligence, educational, psychological, or medical assessment.

Methodology & sources

Define five fixed grids as row and column dimensions, blocked cell indices, and one fixed start. Validate gameplay with a pure state machine that accepts only unused open orthogonal neighbors. Independently enumerate paths by DFS from each start until every open cell is visited; require at least one solution and require the literal declared route to occur in the enumerated set. Simulate all five literal routes through production actions, assert 200 points per clear and exactly 1,000 total, then test invalid no-ops, undo, reset, keyboard movement, repeated-signature deduplication, the second-distinct-error deadlock, restart, and terminal atomicity.

Frequently asked questions

How do I play Fill One Line Puzzle?
Start from the numbered square and extend one continuous path through every open cell. Consecutive cells must share an edge, and no cell can be visited twice.
Can I play with a keyboard or touch screen?
Yes. Drag across adjacent cells on a touch screen or with a pointer. Arrow keys extend the path, Delete undoes, X resets the level, Enter checks, and R restarts.
Are the five levels guaranteed to have solutions?
Yes. Each fixed original grid has a literal valid route, and an independent depth-first search test confirms that every open cell can be covered exactly once from its fixed start.

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