Flip through puzzles with the Next and Prev buttons or the N and P keys. You can work on the puzzles in any order and come back to any puzzle later.
To fill in a puzzle, click on a number on the right and then click on any square to pencil in that number. The rules of Sudoku are that every digit 1-9 must appear once in each row, column, and 3x3 block.
You can also use the keyboard. Point at a square or use arrow ← ↑ ↓ → keys to move the dotted blue rectangle, and then type a digit 1 - 9 to fill it in. Typing multiple numbers in a square will mark all those numbers, but a double-tapped number will clear all marks and write the number as the answer. Use the space or 0 key to clear the selected square again.
The comma , key brings up a menu that lets you mark multiple numbers. With the menu showing, the H key lets you highlight marked numbers in yellow. The M key automatically marks numbers that are not in direct conflict in the row, column, or block, and the Marks button fills these in for every square.
Click a color on the left to reveal squares that are that level of difficulty: violet squares are the easiest, and red squares are the hardest. Click the Color button to reveal all colors.
Hold down the Hint button to get a specific hint. Red squares point out any mistakes. Blue squares will be places that constrain the puzzle in some way, and green squares will be locations where a number can be filled in, or where the possibilities can be narrowed down.
If you are still stuck, you can try a more explicit hint by holding down ctrl while clicking the Hint button. Sometimes the strategies shown will be very subtle: learn to recognize naked pairs and intersections, and see if you can find the hidden pairs or triples or recognize an x-wing, y-wing or swordfish.
The Check button can be used to quickly check if you have penciled in any mistakes or contradictory squares without revealing what the mistakes are.
Holding ctrl while clicking Check will show you the position of a mistake.
When you discover a mistake, you can use the browser's "back" button to undo as many moves as you need to.
The game will keep track of the amount of time it has taken you to solve a puzzle. Press the Timer button to display the elapsed time and hint counter.
If you walk away from a puzzle and don't want all the idle time counted against you, don't worry: press the "Refresh" button in your browser and the timer will go back to the time you made your last move. Similarly, if you save a game, the time saved will be the time of the last move made.
Puzzles can also be saved and loaded using the File button. Saved games are identified by rating, date, and progress, or you can rename them yourself.
If you discover a gem of a game that you would like to share, the Save as Url link will create a short URL for your current puzzle that can be emailed. Any markup and colors you put on the game will be saved along with the URL, so you can share a particularly clever sudoku step with other puzzlers.
If you right-click or hold down ctrl while clicking a square, you can change the puzzle at any time. Holding ctrl while clicking Clear will clear the entire puzzle, and you can enter a new puzzle using the keyboard or mouse. Note that some numbers cannot be entered because the hintpad will not let you enter a puzzle that has no solution.
As soon as you have entered a puzzle with a unique solution, a difficulty rating will be shown and the keyboard will switch back to game mode.
Usually the puzzles found in Heidi's Infinite Sudoku Pad will have 25-30 hints. Naturally, if there are fewer hints, you enjoy a slightly longer game.
The smallest number of hints that can be given on a solvable Suduoku game is believed to be 17, and Gordon Royle maintains a database of all 17-hint puzzles that have been discovered so far. If you hold ctrl while clicking File, one of these 17-hint puzzles will be loaded from the internet.
Sudoku puzzles are rated on a 24-level scale from "Beginner" (the easiest) to "Counfounding" (the hardest). The whole scale:
|
1: Beginner 2: Easy 3: Simple 4: Basic 5: Moderate 6: Tricky |
7: Clever 8: Puzzling 9: Subtle 10: Difficult 11: Knotty 12: Thorny |
13: Baffling 14: Intricate 15: Perplexing 16: Obscure 17: Labyrinthine 18: Obstinate |
19: Abstruse 20: Vexing 21: Enigmatic 22: Formidable 23: Diabolical 24: Confounding |
Puzzles that can be solved by just avoiding direct conflicts are "Basic" or easier, depending on how easy it is to see the constraints. "Subtle" puzzles require one or two clever deductions. And it gets more difficult from there: "Confounding" puzzles involve untangling a mass of complex clues.
Heidi's Hintpad was written in HTML and Javascript by Heidi's husband David Bau using John Resig's jQuery with Ben Alman's handy BBQ plugin (as forked by Edison Wong). Joe Prince's wonderful Handlee font provides handwritten digits and Steve Matteson's Open Sans is used for the puzzle numerals. Jojo Mendoza provided the yellow highlighter icon; and Gordon Royle's mathematically beautiful Minimum Sudoku Collection provides minimal 17-hint puzzles when you hold ctrl while clicking File.
The sources for Heidi's Sudoku Hintpad are not licensed for reuse at this time, but they are available to read here on Github.
Version 0.67