全排列代码实现

去年写不出全排列，今天终于完成，前来还愿

非重复排列

使用分治递归，按位逐层交换，记录底层交换结果，恢复交换并返回

def swap(s, i1, i2):
    if i1 < len(s) and i2 < len(s):
        s[i1], s[i2] = s[i2], s[i1]

def arrange(s, begin, end):
    if begin == end:
        print(s)
        return
    for i in range(begin, end):
        swap(s, begin, i)
        arrange(s, begin + 1, end)
        swap(s, begin, i)

s = [x for x in 'abcd']
arrange(s, 0, len(s))

重复排列

使用进制原理，迭代取余映射，记录映射结果

import numpy as np

def cumdivision(i, base, n):
    arr = []
    while i > 0:
        arr.append(i % base)
        i = i // base
    arr.extend([0] * (n - len(arr)))
    return arr[::-1]

def arrange(s, n):
    base = len(s)
    for i in range(pow(base, n)):
        arr = cumdivision(i, base, n)
        print(np.array(s)[arr])

s = [x for x in 'abcd']
arrange(s, 4)