Python recursion permutations

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You want to do recursion, so you first have to find out how the recursion would work. In this case it is the following:

permutation [a,b,c,...] = [a + permutation[b,c,...], b + permutation[a,c,..], ...]

And as a final condition:

permutation [a] = [a]

So the recursion splits up the list in sublists with one element extracted each time. Then this element is added to the front of each of the permutations of the sublist.

So in pseudo-code:

def permutation(s):
   if len(s) == 1:
     return [s]

   perm_list = [] # resulting list
   for a in s:
     remaining_elements = [x for x in s if x != a]
     z = permutation(remaining_elements) # permutations of sublist

     for t in z:
       perm_list.append([a] + t)

   return perm_list

Does this help?

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