Sudoku By SunSwallow

A sudoku that teaches as it helps. Every puzzle is rated by the hardest step it takes to solve, and every hint explains its reasoning in plain words.

DIFFICULTY YOU CAN TRUST Most sudoku apps grade a puzzle by counting the numbers it starts with. That is why their "easy" can stop you cold while their "hard" falls in ten minutes. Here, each puzzle is solved step by step the way a person would solve it, then rated by the hardest step along the way: • Easy: only the simplest steps, the one number left for a square or the one square left for a number. • Medium: adds pointing pairs and box/line reduction. • Hard: adds pairs and triples. • Expert: adds the X-wing, the Y-wing and the swordfish. No puzzle, at any level, needs a guess. Each has exactly one solution, and logic alone reaches it.

A HINT THAT SHOWS ITS WORKING Stuck? The first press of Hint tells you in plain words where to look and why the step works: which row, column or box, and what rules the other squares out. The second press shades the squares it is talking about. Only the third press does the step for you. It covers every step on the ladder, from the simplest single to the swordfish, and it never runs out.

NOTES BIG ENOUGH TO USE Pencil marks are drawn large and dark, not as faint grey specks. Or turn on automatic notes and the app writes in every square's possible numbers, then keeps them up to date as you play.

A BOARD THAT FITS YOUR HAND The whole grid is on screen at once, with no zooming or scrolling, and the number pad beneath it is built for a sure tap. Tap a square and then a number, or pick a number first and tap every square it belongs in.

MISTAKES, YOUR WAY Have a wrong number marked the moment you place it, only when it repeats in its row, column or box, or never. Undo goes all the way back to the start. There is no clock, no lives and no score.

TODAY'S PUZZLE A new grid every day, the same one for everybody, so a family can work it separately and compare. Skip a day and you lose nothing.

QUIET BY DESIGN There are no ads anywhere in the app and no account to make. It sends no notifications, needs no internet connection and collects no data. It supports VoiceOver and the largest text sizes, and Family Sharing covers the whole household.

Sudoku by SunSwallow is made in Virginia. Send a question or an idea to support@sunswallow.app and a person will write back.

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