Source code for ecgenpy.sjt_list

from typing import Generator




def SJT2(n: int) -> Generator:
    """
    The function `SJT2` generates all permutations of length `n` using the Steinhaus-Johnson-Trotter
    algorithm.

    :param n: The parameter `n` represents the number of elements in the permutation
    :type n: int
    :return: The function `SJT2` is a generator function, which means it yields values instead of
    returning them. It generates all permutations of length `n` using the Steinhaus-Johnson-Trotter
    algorithm. Each permutation is represented as a list of integers.
    """
    if n == 2:
        yield [0, 1]
        yield [1, 0]  # tricky part: return to the origin
        return

    gen = SJT2(n - 1)
    up = range(n)
    down = range(n - 1, -1, -1)

    for pi in gen:
        for i in down:  # downward
            yield pi[:i] + [n - 1] + pi[i:]
        pi = next(gen)
        for i in up:  # upward
            yield pi[:i] + [n - 1] + pi[i:]



# def main():
#     fruits = list("🍉🍌🍇🍏")
#     print(" 0 1 2 3")
#     for lst in SJT2(4):
#         mylst = list(fruits[i] for i in lst)
#         print("".join(mylst))
#
#
# if __name__ == "__main__":
#     main()