Hidato

Hidato (also known as Hidoku) is a logic puzzle where the player must fill a grid with consecutive numbers that connect to each other horizontally, vertically, or diagonally. The grid contains some pre-filled numbers as clues, and the solver must create a continuous path from the lowest to the highest number, visiting every cell exactly once. Each number must be adjacent (including diagonals) to the numbers immediately before and after it in the sequence.

Rules

1. Fill every cell in the grid with a number from 1 to the total number of cells.
2. The number 1 and the highest number are always given as starting and ending clues.
3. Additional numbers are pre-placed as clues throughout the grid.
4. Each number must be adjacent (horizontally, vertically, or diagonally) to the next consecutive number.
5. Every cell must be filled — the path visits each cell exactly once.

Strategies

• Work from Given Numbers: Start by identifying pairs of given numbers that are close together in value. If two given numbers (say 5 and 7) are near each other on the grid, there must be exactly one cell between them in the path, and that cell must be adjacent to both.
• Forced Paths: If a given number has only one unoccupied neighbor that could be the next (or previous) number, the path is forced through that neighbor.
• Bottleneck Detection: Look for narrow passages in the grid where the path must pass through. If there is only one way to connect two parts of the grid, those intermediate cells are determined.
• Counting Available Cells: Between two given numbers, count how many cells are needed versus how many are available. If the count matches exactly, the path through that region is forced.
• Dead-end Avoidance: Avoid creating isolated cells that cannot be reached. If placing a number would cut off an unvisited cell from the rest of the path, that placement is wrong.
• Diagonal Awareness: Unlike many grid puzzles, diagonal adjacency counts. This gives each cell up to 8 neighbors instead of 4, which affects path flexibility.

Hidato was invented by Dr. Gyora Benedek, an Israeli mathematician and entrepreneur. Benedek created the puzzle in 2007 and trademarked the name "Hidato," which comes from the Hebrew word "hida" (חידה), meaning "riddle" or "puzzle."

The puzzle was first published in 2008 and quickly gained international attention. It appeared in newspapers across Europe and the United States, including syndication deals with several major media outlets. Benedek founded a company to promote and distribute Hidato puzzles worldwide.

Hidato belongs to the family of Hamiltonian path puzzles — problems where the solver must find a path that visits every node exactly once. This connects it to a rich tradition in mathematics and computer science. The Hamiltonian path problem is famously NP-complete in general graphs, but the specific structure of Hidato grids (with given clue numbers constraining the path) makes most puzzles solvable through human-accessible logic.

The puzzle has been compared to Numbrix, a similar puzzle created by Marilyn vos Savant for *Parade* magazine, which uses the same consecutive-number mechanic but only allows horizontal and vertical adjacency (no diagonals). Hidato's inclusion of diagonal connections gives it a different character, with more flexible paths and a distinct solving feel. Both puzzles remain popular in newspapers and puzzle apps worldwide.