經典數獨

Daily Sudoku: rules and solving techniques

Complete the 9×9 grid and train your logic and focus. This guide reflects the controls and win conditions in the current browser build. It is reviewed by the PocketJoy game-testing team and maintained by Long-Term New Media Limited.

Puzzle rules

Fill a 9×9 grid with the digits 1 to 9 so that each row, each column and each 3×3 box contains every digit exactly once — those three simultaneous constraints are the entirety of the rules. The given numbers cannot be changed and the game blocks any attempt to alter them, so the remaining cells must be worked out by logic. Three difficulty levels set how many digits are given and how deep the required reasoning goes: the easy setting usually yields to basic single-candidate reasoning, while the hard one demands candidate elimination and techniques such as naked pairs. You are allowed three incorrect entries per game, after which it ends with an offer of a fresh puzzle; that cap preserves some tension while discouraging brute force in place of deduction. Your time is recorded and a fastest result is stored for each difficulty on your device.

Reasoning and solving techniques

The two most basic and most effective techniques are the naked single and the hidden single. For the first, look at an empty cell: if its row, column and box between them already contain eight different digits, the remaining digit is the answer. The second works the other way round: if within a box the digit 7 can only go in one cell, that is its position, even if the cell has other candidates of its own — and this one is used more often, frequently opening a grid that looks entirely opaque. Harder puzzles need candidate elimination, listing every possible digit for each cell and then removing them by structured patterns. The most useful advanced technique is the naked pair: if two cells in the same row, column or box share exactly the same two candidates, say {3,7}, those two digits must occupy those two cells between them, and 3 and 7 can be removed from every other cell in that unit. Naked triples extend the idea. When scanning, work digit by digit, starting with the one that already appears most often, since more placements mean stronger constraints and easier hidden singles.

Easy mistakes to make

The most common mistake is guessing. Every cell in a sudoku is deducible, and a wrong guess not only spends one of your three allowances but builds all your later reasoning on a false foundation, with the contradiction often surfacing so late that its source can no longer be identified. The second is fixating on the row with fewest empty cells, when you should be applying row, column and box constraints together, since many answers only appear where all three intersect — and it is precisely that triple intersection that makes sudoku more interesting than a plain Latin square. The third is attempting the hard level without marking candidates, which mid and high difficulties effectively require, since holding nine possibilities across many cells quickly exceeds working memory. The fourth is rescanning the same region when stuck. The right move is to change dimension: if reading by cell reveals nothing, read by digit and ask where that digit can still go in this box; and if that fails too, concentrate on the cells with fewest candidates.

Who will enjoy it

A natural fit for anyone who enjoys pure deduction, and the most widely played number puzzle in the world. There is no luck involved, every puzzle has a unique solution, and every cell is deducible without guessing — a certainty that makes it a fixture of many people's commute or bedtime routine. Its ancestor is the Latin square studied by the Swiss mathematician Euler in the eighteenth century; the modern form was designed by Howard Garns in the United States and published as Number Place in 1979, reached Japan in 1984 where it acquired the name sudoku, meaning that the digits must remain single, and swept the world after the Times introduced it to Britain in 2004. It has been proved mathematically that a grid needs at least seventeen givens to guarantee a unique solution. The easy level is relaxing while the hard one requires techniques such as naked pairs, and a game runs ten to thirty minutes.

Helper features

Three difficulties set how many digits are given and how deep the required reasoning goes, with a fastest time stored for each so they never overwrite one another. The run panel shows the timer and your current mistake count — three errors are allowed per game, and that cap is the key design decision here: it preserves tension while preventing brute force from substituting for deduction, since without a limit anyone could complete any grid by repeated trial and the point of a logic puzzle would be lost. The mistake count updates live so you always know how much margin remains, which genuinely affects whether to risk an uncertain digit on a hard grid. A regenerate button produces a fresh puzzle at any time rather than only after the current one ends. A failed game states plainly that the mistake limit was reached and encourages a new attempt rather than merely displaying a failure screen, and completion shows your total time.

Controls and saved progress

Tap a cell and then choose the digit to enter; the given numbers cannot be modified and the game blocks attempts directly, so the puzzle itself can never be altered by accident. Mouse and touch follow identical logic, and cells and number keys are large enough for one-handed use on a phone with no system keyboard required, so a whole grid can be solved single-handed. To change one of your own entries, select the cell again and enter a new digit, which overwrites without needing to clear first. A fastest time per difficulty is stored in the browser's local storage on your own device, with no account required and nothing uploaded to any server; records do not travel to another device, and clearing browser data removes them. The language button switches the interface between Traditional Chinese and English instantly, updating every panel label and prompt without a page reload. Once the page has loaded, the game itself plays offline.

Solving FAQ

There is a dedicated primer: A Complete Beginner Guide to Sudoku.

Reviewed by the PocketJoy game-testing team · Operated by Long-Term New Media Limited · hklongtermad@gmail.com