Crosswords and Swedish-Style Crosswords: Three Great Algorithms to Choose From
A densely packed grid, the familiar classic look, or an extra-elegant design without any black separator bars? Puzzle-Generator gives you three different generation algorithms for crosswords and Swedish-style crosswords – and you decide with a single click which one builds your puzzle. In this article you'll learn how the three variants work, how they differ, and when each one is the best choice.
In this article
- Why your choice of algorithm changes the puzzle
- What makes a good puzzle grid?
- The three algorithms at a glance
- Backtracking algorithm (default) – the all-rounder
- Classic algorithm – proven and predictable
- No-blocker algorithm – for the most elegant look
- How to select the algorithm in the generation settings
- Which algorithm should you use when?
- Tips for even better results
Why your choice of algorithm changes the puzzle
When you click Generate in Puzzle-Generator, something fascinating happens behind the scenes: within a fraction of a second, the program tries out thousands of ways to arrange your words in the grid so that they cross each other as often as possible and the available space is well filled. The strategy used to achieve this is called an algorithm – and this is exactly where you get to choose.
Each of the three algorithms pursues a different goal: maximum grid density, predictable behavior, or a particularly tidy appearance without any black separator bars at all. Depending on your choice, the finished puzzle looks noticeably different – with the exact same word list!
The best part: you don't need to understand any of the technology. All you need to know is what kind of result you want. Our step-by-step guide Create a crossword puzzle shows you how to build a puzzle from scratch – this article dives deeper into the most exciting step: generation.
What makes a good puzzle grid?
Three simple characteristics determine whether a crossword looks professional.
Many intersections
The more often horizontal and vertical words cross each other, the more interwoven and high-quality the puzzle feels – and the more solving hints your puzzlers get. Intersections are the heart of every good crossword.
High fill rate
A good grid has as few empty, unused cells as possible. Large gaps make a puzzle look unfinished. The algorithms differ significantly in how completely they fill the available area with words.
Few separator bars
So-called blockers are black bars that separate two words that would otherwise run into each other unintentionally. Fewer blockers mean a calmer, tidier puzzle layout – and only the no-blocker algorithm gets rid of them entirely.
The three algorithms at a glance
A quick comparison before we look at each algorithm in detail.
| Characteristic | Backtracking (default) | Classic algorithm | No-blocker algorithm |
|---|---|---|---|
| Grid fill rate | Very high – fills the grid most completely | Good, but may leave more empty cells | High, slightly looser by design |
| Intersection density | Very high | High | High – deliberately favors multiple crossings |
| Black separator bars (blockers) | Very few | Few to some | None at all |
| Appearance | Dense and compact | Classic, familiar from earlier program versions | Particularly clean and elegant |
| Number of placed words | Maximum | High | Somewhat lower than the default |
| Recommendation | The best choice for most puzzles | When you want proven, predictable behavior | When looks and design come first |
All three algorithms are available for crosswords and Swedish-style crosswords – both with clue texts shown directly in the grid cells (typical for Swedish crosswords) and with numbers plus a separate clue list (classic crossword style).
Backtracking algorithm (default) – the all-rounder
The backtracking algorithm is the most modern and most powerful of the three variants – which is why it is preselected in Puzzle-Generator. Its name reveals the secret: backtracking means the algorithm can take back decisions it has already made. Whenever it runs into a dead end while filling the grid, it selectively removes individual words, moves them to better positions, and repairs the resulting gaps.
How it works – in plain words
Imagine a patient jigsaw puzzler who doesn't just stubbornly place piece after piece, but occasionally takes three pieces back out when he notices that something better is possible in one spot. That's exactly what the built-in displacement and repair strategies do: they detect poorly filled regions, dissolve them, and refill them – until the grid is almost completely occupied.
- Advantage: The fullest grid of all three variants – with good word lists, well over 50 % of the letters cross a second word.
- Advantage: Places the most words from your list and needs only very few black separator bars.
- Option: Individual, isolated words without cross-references can be omitted – every word is woven into the puzzle.
- Good to know: Because of the many optimization steps, generation takes slightly longer than with the classic algorithm – in practice usually just a few seconds.
Classic algorithm – proven and predictable
The classic algorithm is the original: countless puzzles were created with it in earlier versions of Puzzle-Generator. It works on the principle of "best word in the best free spot" – word by word, without rearranging words that have already been placed.
When its strengths pay off
Precisely because it skips elaborate rebuilding strategies, its behavior is particularly predictable: same word list, similar grid layout. If you've been working with Puzzle-Generator for years and appreciate the familiar puzzle character, you'll feel right at home here.
- Advantage: Very fast and resource-friendly – ideal for large grids and long word lists.
- Advantage: Predictable, consistent results – the familiar puzzle look of earlier program versions.
- Keep in mind: Without repair strategies, more empty cells may remain in the grid than with the backtracking default. Tip: simply generate several times and keep the best result.
No-blocker algorithm – for the most elegant look
This algorithm follows an uncompromising design idea: not a single black separator bar in the entire puzzle. Words end exclusively at the grid edge or at a clue cell – never at a black bar. The result is an exceptionally calm, high-quality puzzle layout that contains nothing but letter cells and clue cells.
Smart placement instead of separator bars
Without blockers, the algorithm cannot allow itself any "quick fixes" – every word position must be cleanly bounded from the start. To achieve this, it plans in several passes: first it builds a strongly interwoven framework of words with multiple crossings, then it fills the remaining areas in a targeted way. Throughout, it consistently prefers positions where a word crosses two or three existing words at once.
- Advantage: The cleanest, most refined appearance – perfect for gifts, wedding newspapers, high-quality print products, and any puzzle where design comes first.
- Advantage: Deliberately favors multiple crossings – the placed words are particularly tightly interwoven.
- Keep in mind: The strict design rule comes at a price – usually somewhat fewer words fit into the grid than with the default algorithm, and individual areas may remain empty. For a densely packed puzzle with the maximum number of words, the backtracking default is the better choice.
How to select the algorithm in the generation settings
Switching between the three algorithms is deliberately simple – a single dropdown is all it takes:
- Open your crossword project and switch to the 2. Generate area.
- Open the generation settings (generation options).
- In the Algorithm dropdown, choose one of the three variants: Backtracking algorithm (default), Classic algorithm, or No-blocker algorithm. A short description right below the dropdown explains at any time what the selected variant does best.
- Confirm and click Generate – done!
A tip from experience: generate the same puzzle once with each algorithm and compare the results side by side. For more impressions of the user interface, take a look at our screenshot gallery of the Puzzle-Generator app.
Which algorithm should you use when?
The right choice depends on what you want to use your puzzle for – here's the quick decision guide.
Backtracking (default)
Your choice when in doubt. Maximum grid density and word count – the best all-round quality.
- Puzzle magazines, periodicals, and publishers
- Worksheets for school and teaching
- Puzzles with many words in limited space
- Anyone who simply wants the best overall result
Classic algorithm
Your choice for the tried and true. Fast, consistent, and familiar – the original from earlier versions.
- Quick drafts and intermediate versions
- Very large grids and extensive word lists
- Long-time users who appreciate the familiar puzzle character
- Puzzle series with a uniform, recognizable grid style
No-blocker
Your choice for looks. Not a single black bar – the most elegant puzzle layout.
- Personal gifts for birthdays and weddings
- High-quality print layouts and customer magazines
- Puzzles with a background image or special design
- Anyone who wants a particularly clean, calm grid
Want to see what finished puzzles look like with different settings? Our puzzle examples with free downloads include Swedish-style crosswords, classic crosswords, and more – as PDF, image, or vector graphics.
Tips for even better results
How to get the most out of each of the three algorithms.
Generating multiple times always pays off
All three algorithms use elements of randomness – every generation run produces a different grid. Simply create several variants in a row and keep the most beautiful one. With the classic and the no-blocker algorithm in particular, this often makes the decisive difference.
Put together the right word list
A mix of short words (3–5 letters) and long terms gives every algorithm the best building material. Short words fill gaps, long words form the backbone with many intersection points. The guide on creating a crossword puzzle shows you how to set up and import word lists.
Enable fill words
Let Puzzle-Generator add suitable fill words from its built-in word library alongside your own terms. All three algorithms benefit from this – the grid becomes denser without you having to type in hundreds of words yourself.
Algorithm first, fine-tuning second
First pick the algorithm and generate a grid you like – only then take care of colors, fonts, and export. All output formats from PDF to PNG to SVG are available with every algorithm; for a comparison of the export options in each version, see the overview of Puzzle-Generator editions.
Still have questions about generation or the settings? It's worth taking a look at the frequently asked questions (FAQ) – the most important topics around the Puzzle-Generator app are answered there in a compact form.
Try all three algorithms yourself!
Backtracking, classic, or no-blocker? The most fun way to decide is to compare them with your own words: download Puzzle-Generator for free, generate your crossword or Swedish-style crossword with each of the three algorithms, and find your favorite – in just a few minutes, no prior knowledge required.
Download nowBy the way: besides crosswords, Puzzle-Generator also lets you create word search puzzles – a great addition for teaching, events, and puzzle booklets.