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Killer Sudoku

Complete a fixed, uniquely solvable Killer Sudoku by combining familiar row, column, and box logic with connected cage sums.

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How to use

  1. 1.Select one of the nine empty cells, then enter a digit with the on-screen 1 through 9 controls or the matching number key.
  2. 2.Make every row, column, and 3 by 3 box contain 1 through 9 once while each connected cage reaches its target without a repeated digit.
  3. 3.Fill every blank and press Enter or Check grid; correct the first wrong completed attempt before a second error deadlocks the run.

About Killer Sudoku

Killer Sudoku combines ordinary Sudoku placement rules with arithmetic cages. Every row, every column, and every bold 3 by 3 box must contain digits 1 through 9 exactly once. Each outlined cage also has a small target number: the digits in that cage must add to the target, and a digit cannot repeat within the same cage. This page publishes one fixed product-authored 9 by 9 fixture so the rules, clues, solution, and behavior remain reproducible on every restart.

The board begins with 72 givens and nine empty cells. Select an empty cell, then use the number controls or press a number key from 1 through 9. Arrow keys move among editable cells. Backspace or Delete clears the selected entry. When all nine blanks contain a digit, press Enter or choose Check grid. An incomplete check shows a reminder but does not consume a mistake. This makes accidental early checks harmless and keeps the attempt policy explicit.

A completed correct grid earns exactly 1,000 points. The first incorrect completed grid remains editable, so you can inspect the rows, columns, boxes, and cages and repair the entry. A second incorrect completed check deadlocks the run until Restart. Completed and deadlocked states are terminal: number input, clearing, cursor changes, and further checks cannot alter the score or result. Restart clears all nine player entries, the mistake count, feedback, score, and terminal state while preserving the same published givens.

The fixture is deliberately stable rather than randomly generated. The completed solution is checked independently as a valid Sudoku grid. Tests then inspect every cage. All 81 cells must appear exactly once across 27 cages, no cage may overlap another, each cage must be orthogonally connected, its target must equal the sum of the corresponding solution digits, and its solution digits must not repeat. A four-neighbor graph traversal supplies the connectivity check instead of assuming that consecutive array positions are adjacent.

Uniqueness is also verified rather than inferred from the visible number of givens. An independent backtracking counter starts from the published 72 givens and tries candidate digits in each blank. During the search it rejects duplicate digits in rows, columns, and 3 by 3 boxes. It separately rejects repeated cage digits, sums above a cage target, and completed cages whose sum misses the target. The release test requires the combined constraint system to produce exactly one complete solution. This protects the route from publishing an ambiguous or contradictory fixture.

A practical solving route is to begin with the familiar Sudoku units. For an empty cell, compare the digits already present in its row, then remove digits already present in its column and box. The cage total provides another cross-check. If a cage has two known digits and one blank, subtract the known values from the small target. Confirm that the remaining digit does not duplicate another digit in the cage and still satisfies the row, column, and box before entering it. Because this fixture has one blank in each row, many placements can be confirmed directly, while the cage clue catches arithmetic inconsistencies.

The interface is designed for pointer, touch, and keyboard use. Every editable cell is a real button with a row-and-column accessibility label. The nine input controls maintain touch-friendly height, and the 9-column board uses zero-minimum fractional tracks so it stays inside a narrow mobile viewport instead of forcing horizontal overflow. The selected cell has a visible focus-style outline. The site's shared Restart control is always available, and the shared double-Escape boss key temporarily replaces play with a spreadsheet-style view; double-Escape again returns to the unchanged game.

All state transitions run in the current browser tab. The game does not upload the grid, call a puzzle API, generate a remote board, request an account, or add a new client dependency. If local storage is available, only the best completed score is retained through the site's existing game shell. The puzzle givens and cages are original product fixtures. The linked rule sources support the public rule definitions only; this page does not claim that its board was published or endorsed by either source.

This Killer Sudoku is casual entertainment and transparent logic practice. It is not a standardized intelligence, educational, aptitude, psychological, or clinical assessment. The score measures whether this one fixed fixture was completed within the stated two-error route. It should not be used to compare people or make decisions about learning, employment, health, or ability. For a different local challenge, the related games offer shaded-grid deduction, arithmetic fill-ins, compact number placement, and clue-based path reasoning.

Methodology & sources

The published fixture stores a complete product-authored Sudoku solution, removes nine fixed cells to form the playable givens, and partitions all 81 cells into 27 connected three-cell cages. Fixture validation requires a valid 1 through 9 solution in every row, column, and 3 by 3 box; an exact non-overlapping cage cover; orthogonal cage connectivity; target sums matching the solution; and no repeated solution digit within a cage. An independent backtracking counter begins with the published givens, applies Sudoku uniqueness and partial or complete cage constraints at every candidate, stops after two solutions, and is required to return exactly one. Runtime checking does not count incomplete submissions, allows one incorrect completed check, deadlocks on the second, awards exactly 1,000 for the valid complete grid, and freezes all terminal state transitions.

Frequently asked questions

What rules does this Killer Sudoku enforce?
It enforces digits 1 through 9 exactly once in every row, column, and 3 by 3 box, plus each cage's target sum and no repeated digit within a cage.
Does the published puzzle have one solution?
Yes. A separate backtracking test counts solutions under the Sudoku and cage constraints together and requires exactly one for the released fixture.
Does checking an incomplete grid use a mistake?
No. Incomplete checks only show a reminder. The first incorrect completed grid can be repaired, while a second incorrect completed check deadlocks the run.
Can I play on mobile or with a keyboard?
Yes. The board uses a non-overflowing nine-column mobile layout. Number keys enter digits, arrows move among blanks, Delete clears, and Enter checks.

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