python回溯法实现数组全排列输出

"""
皮蛋编程(https://www.pidancode.com)
创建日期：2022/3/30
功能描述：python回溯法实现数组全排列输出
"""
from sys import stdout


def perm(li, start, end):
    if (start == end):
        for elem in li:
            stdout.write(elem)
        print('')
    else:
        for i in range(start, end):
            li[start], li[i] = li[i], li[start]
            perm(li, start + 1, end)
            li[i], li[start] = li[start], li[i]


if __name__ == '__main__':
    li = ['a', 'b', 'c', 'd']
    perm(li, 0, len(li))