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  1. # Generate successive k-length permutations. (4.00)
  2. # @note Rewrite of the code that appears at
  3. # docs.python.org/3/library/itertools.html#itertools.permutations
  4. # (restores indirect indexing)
  5. # @see 3UOMj3, vSELdo, cTaz9y
  6.  
  7. def permutations(iterable, k=None):
  8.     pool = tuple(iterable)
  9.     n = len(pool)
  10.     if k is None:
  11.         k = n
  12.     elif k > n:
  13.         return
  14.     index = list(range(n))
  15.     cycle = list(range(k))
  16.  
  17.     while True:
  18.         yield tuple(pool[i] for i in index[:k])
  19.         for i in reversed(range(k)):
  20.             j = cycle[i] + 1
  21.             if j < n:
  22.                 cycle[i] = j
  23.                 index[i], index[j] = index[j], index[i]
  24.                 break
  25.             cycle[i] = i
  26.             index.append(index.pop(i))
  27.         else:
  28.             return
  29.  
  30. # Test.
  31.  
  32. import itertools
  33. import time
  34.  
  35. n = 3
  36. a = list(range(n))
  37. for k in range(2+len(a)):
  38.     print(list(permutations(a, k)))
  39.     print(list(itertools.permutations(a, k)))
  40.  
  41. def test(f, a):
  42.     t = time.process_time()
  43.     for _ in f(a):
  44.         pass
  45.     t = time.process_time() - t
  46.     print('Elapsed: {:.6f}s'.format(t))
  47.     m = sum(1 for _ in f(a))
  48.     n = sum(1 for _ in itertools.permutations(a))
  49.     assert m == n
  50.     for x, y in zip(f(a), itertools.permutations(a)):
  51.         assert x == y
  52.  
  53. n = 8
  54. a = list(range(n))
  55. test(permutations, a)
  56. test(itertools.permutations, a)
Success #stdin #stdout 0.31s 14080KB
comments (?)
stdin 
Standard input is empty
stdout 
[()]
[()]
[(0,), (1,), (2,)]
[(0,), (1,), (2,)]
[(0, 1), (0, 2), (1, 0), (1, 2), (2, 0), (2, 1)]
[(0, 1), (0, 2), (1, 0), (1, 2), (2, 0), (2, 1)]
[(0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), (2, 1, 0)]
[(0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), (2, 1, 0)]
[]
[]
Elapsed: 0.065700s
Elapsed: 0.004203s
https://ideone.com/GAA7sc
language:
Python 3 (python  3.12)
created:
1 day ago
visibility:
public

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