一、模块

python模块实现排列和组合

组合

from itertools import combinationss = "123456"print(list(combinations(s, 4)))# [('1', '2', '3', '4'), ('1', '2', '3', '5'), ('1', '2', '3', '6'), # ('1', '2', '4', '5'), ('1', '2', '4', '6'), ('1', '2', '5', '6'), # ('1', '3', '4', '5'), ('1', '3', '4', '6'), ('1', '3', '5', '6'), # ('1', '4', '5', '6'), ('2', '3', '4', '5'), ('2', '3', '4', '6'), # ('2', '3', '5', '6'), ('2', '4', '5', '6'), ('3', '4', '5', '6')]

combinations(iterable,r)
iterable:可迭代对象，需要组合的对象
r:需要组合的位数
2. 排列

from itertools import permutationss = "123456"print(list(permutations(s, 2)))# [('1', '2'), ('1', '3'), ('1', '4'), ('1', '5'), ('1', '6'), ('2', '1'), # ('2', '3'), ('2', '4'), ('2', '5'), ('2', '6'), ('3', '1'), ('3', '2'), # ('3', '4'), ('3', '5'), ('3', '6'), ('4', '1'), ('4', '2'), ('4', '3'), # ('4', '5'), ('4', '6'), ('5', '1'), ('5', '2'), ('5', '3'), ('5', '4'), # ('5', '6'), ('6', '1'), ('6', '2'), ('6', '3'), ('6', '4'), ('6', '5')]

permutations(iterable,r)
iterable:可迭代对象，需要排列的对象
r:需要排列的位数

二、python实现

来源于官网，效率不如模块

组合

def combinations(iterable, r):    pool = tuple(iterable)    n = len(iterable)    if r > n:        return    indices = list(range(r))    yield tuple(pool[i] for i in indices)    while True:        for i in reversed(range(r)):            if indices[i] != i + n - r:                break        else:            return        indices[i] += 1        for j in range(i + 1, r):            indices[j] = indices[j - 1] + 1        yield tuple(pool[i] for i in indices)

if __name__=='__main__':
    cl="123456789"
    r=5
    clist=list(combinations(cl, r))
    print(f'组合数的个数为{len(clist)}。')
    print('它们是:\n',clist)

排列

def permutations(iterable, r=None):    pool = tuple(iterable)    n = len(iterable)    r = n if r is None else r    if r > n:        return    indices = list(range(n))    cycles = list(range(n, n - r, -1))    yield tuple(pool[i] for i in indices[:r])    while n:        for i in reversed(range(r)):            cycles[i] -= 1            if cycles[i] == 0:                indices[i:] = indices[i + 1:] + indices[i:i + 1]                cycles[i] = n - i            else:                j = cycles[i]                indices[i], indices[-j] = indices[-j], indices[i]                yield tuple(pool[i] for i in indices[:r])                break        else:            return

if __name__=='__main__':
    pl=[1,2,3,4,5,6,7,8,9]
    r=3
    plist=list(permutations(pl, r))
    print(f'排列数的个数为{len(plist)}。')
    print('它们是:\n',plist)

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