C program to generate all permutations

The Mutex is there just to ensure things don't get screwed when the execution is asynchronous notice that you can pass an UnsafeAction parameter that will in turn get a pointer to the permuted array. You must not change the order of elements in that array pointer! If you want to, you should copy the array to a tmp array or just use the safe action parameter which takes care of that for you - the passed array is already a copy.

Note: I have no idea how good this implementation really is - I haven't touched it in so long. Lu4 What's awful about it? The more optimizations, the less beautiful the code - but it runs lightning fast.

Your original implementation provided in your question is the best solution here. It's clean and fast code and generates sorted permutation.

I'd never use this marked as answer actually I'm actually studying your original solution, I had the same intuitions you had but I did not manage to code a general solution. Well done. But the topic was really making it as efficient as possible even at the cost of readability , which this solution provided best for me. Also, your code is unsafe. When you test, if you put null as Action, how could you tell that compiler optimization will not throw away the reading of yield the real calculation of permutation?

Evaluate items, Evaluate ; Console. Sam Sam 1, 2 2 gold badges 20 20 silver badges 30 30 bronze badges. I saved items. Count to a variable. The fact is, you're doing 2N! I would expect at least a x1. On 12 elements it takes ms compared to ms. The order isn't strictly lexicographical either. Show 9 more comments. WriteLine label ; Console. There are n! Ziezi Ziezi 6, 3 3 gold badges 34 34 silver badges 46 46 bronze badges.

Nice and neat solution for general purposes. However in terms of speed it falls behind. Using closure will maybe somewhat make it faster, but only by a tiny bit. I would imagine that it only saves a few stack operations of copying the pointer to the array, and little stuff like that - nothing significant, though. The second idea you've suggested - using a boolean array - might make a good change! I'll try that and come back to you : — SimpleVar. The bools idea didn't turn out to be helpful at all I still need to compare non-neighbor values when searching for the "swap partner" in the "tail", and accessing a bool in an array isn't much different than comparing two integers.

Managing a second array wasted time in this case. But nice idea. YoryeNathan But you are now in a position to try other things.

For instance loop unrolling. Emit a perm. Then swap the last two and emit the next perm. Then go back to your more complex logic, secure in the knowledge that you know the last two elements are reversed. This skips the full logic for half of perms, and skips one comparison for the other half of perms.

You can try unrolling farther - at some point you'll hit cache issues and it will not be worthwhile. That's a nice idea, but I doubt it will matter that much. It basically saves me just a few variables declared and stepping in and immediately out of two loops, and a single comparison between two elements. Turns out I was wrong, it was a great idea! It cuts the time in by much! Waiting to see if any thing better comes up, and considering marking this as the answer.

Colonel Panic Colonel Panic k 77 77 gold badges silver badges bronze badges. The link is broken for me, although Google finds that website as well, so it's weird. Pinging to it in CMD results with timed-outs, so I can only guess the link is actually broken.

I think the author's website is down. Resort to Amazon, or your library. MattHickford The book has some good information there, but nothing that can practically help me.

I imagine Knuth is comprehensive but I don't have a copy. I didn't hear of Knuth algorithm before, but turns out my algorithm is pretty much his. I created an algorithm slightly faster than Knuth's one: 11 elements: mine: 0. Antoine Comeau Antoine Comeau 3 3 silver badges 7 7 bronze badges. Seems interesting, though it seems to be somewhat slower than my current implementation marked as answer.

I'd love to understand it, though. Since we talk about performance, get rid of the jagged arrays and use stride instead. As the author of this question was asking about an algorithm: [ Steinhaus—Johnson—Trotter algorithm on Wikipedia Beautifully explained here. It's 1 am and I was watching TV and thought of this same question, but with string values.

Given a word find all permutations. Generating permutations of all elements of an array Oct. Become an Author Submit your Article. It's Simple and Conceptual. Get Python course for Days Hours Min Sec. Pro Course Features. Simple Videos. Questions to Practice. Solved Examples. Certificate of Completion. Discussion with Experts. We're Hiring.

Thus the numbers obtained by keeping 1 fixed are: Now, we have all the numbers which can be made by keeping 1 at the first position. Thus the numbers obtained are: Now, we will fix 3 out of 2, 3 and 4. So, you have understood the logic of making the permutations. Now, let's the code for the same.

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When a sequence of instructions is executed in a repeated manner, it is called a loop. Example : :. Notify of. Inline Feedbacks. Previous Print reverse of a string using recursion. Next Print all distinct permutations of a given string with duplicates. Recommended Articles. Generate all binary permutations such that there are more or equal 1's than 0's before every point in all permutations. Number of permutations of a string in which all the occurrences of a given character occurs together.

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