Algorithms

heap.py

# Python3 implementation of Heap's algorithm
# https://en.wikipedia.org/wiki/Heap%27s_algorithm
def heap(lst, k=None):
    if k is None: k = len(lst)
    if k == 1: 
        yield(tuple(lst))
        return
    yield from heap(lst, k - 1)
    for i in range(k-1):
        m = i if k % 2 == 0 else 0
        lst[m], lst[k-1] = lst[k-1], lst[m]
        yield from heap(lst, k-1) 
   
# Test
from itertools import permutations
result = list(heap(list(range(5))))
set(permutations(list(range(5)))) == set(result)