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POGenerate all permutations of a list in lexicagraphical order
 

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  1. POGenerate all permutations of a list in lexicagraphical order
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    <p>I am very much a beginner. I am trying to write a program that, given the number of elements (1-9) in the list as a parameter, will then output all permutations of the list in lexicographical order. In the program it is adding on each permutation as a list into a larger list that contains all the permutations in order. Although the program is not working as expected in general, one main problem I'm having is with this while loop In line 10, I want the list to stop compiling once the final permutation has been added to the list. For example, if my input parameter is n = 4, the last permutation/element should be [4,3,2,1]. However, when I run this program, that element is in the list three times at the end. I don't know how this is so when it should terminate that while loop once it has been added.</p> <pre><code>def ourPermutations(n): x=list(range(1,n+1)) permList = [] permList+=[x] xcopy = x[:] finalPerm = xcopy[::-1] while x != finalPerm: istar = n-2 while x[istar] &gt; x[istar+1]: istar -= 1 jstar = n-1 while x[jstar] &lt; x[istar]: jstar -= 1 x[istar],x[jstar] = x[jstar],x[istar] if istar+1 == n-1: x = x[:] else: a = x[istar+1:] a = a[::-1] x = x[:istar+1] + a permList += [x] return permList </code></pre> <p>That is my main question; however, this program is still missing elements when I run it. It isn't quite working, so if you see a spot where something is obviously wrong, feel free to tell me that particular line is what is causing my problems. If it helps, this is based on this identical (and correct) version written in Mathematica 8:</p> <pre><code>ourpermutations[n_] := ( ourlist = {x=Range[1,n]}; While[ x != Reverse[Range[1,n]], istar = n-1; While[x[[istar]] &gt; x[[istar+1, istar--]; jstar = n; While[x[[jstar]] &lt; x[[istar]], jstar--]; x[[{istar, jstar}]] = x[[{jstar, istar}]]; AppendTo[ourlist, x = Join[Take[x,istar], Reverse[Drop[x,istar]]]] ]; ourlist ) </code></pre> <p>So this is what my Python code should be doing; I just can't get it to do so just yet. Thanks for any of your time and effort.</p>
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    1. USpomzer
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    1. CONot an answer, but, `itertools.permutations()` might be helpful in case you don't care about the implementation.
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      1. USSukrit Kalra
    2. COWhat is the output of `ourPermutations(3)` supposed to look like?
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    3. COThanks, but a professor just asked us to try and see if we could get this to work in other languages. The output should look like this: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
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