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Kamorivs.shvedaction

Calculate permutations by their index number on sorted list of all permutations

Mathematics
Algorithms
Logic
Numbers

I don't understand kumites, so sorry if this isn't what you wanted

Original Description:
If we have planty of objects like this: ['a', 'b', 'c']
then we can build all permutation:

0 – abc
1 – acb
2 – bac
3 – bca
4 – cab
5 – cba
Any of them permutations may be calculated by their index number without calculated others.

Code
Diff
  • from itertools import permutations

def SequencePermutation(plenty, count):
    ret = list(permutations(plenty, count))
    return ret
    • import math
    • from itertools import permutations
    • def SequencePermutation(plenty, count):
    • ret = list(permutations(plenty, count))
    • return ret
    • class SequencePermutation(object):
    • def __init__(self, plenty_object, count_item):
    • self.plenty_object = list(plenty_object)
    • self.count_item = count_item
    • self.power_plenty = len(plenty_object)
    • @staticmethod
    • def calc_count_permutation(n, k):
    • return int(math.factorial(n) / math.factorial(n - k))
    • def __getitem__(self, index):
    • current_mod = index
    • plenty = self.plenty_object.copy()
    • for i in range(self.count_item - 1):
    • perm_count = self.calc_count_permutation(self.power_plenty - i - 1, self.count_item - i - 1)
    • current_index = current_mod // perm_count
    • yield plenty[current_index]
    • plenty.pop(current_index)
    • current_mod = current_mod % perm_count
    • yield plenty[current_mod]