获取字符串全排列 或者 只输出k个的组合

已知长度为n的字符串，获取所有可能的全排序 n!

def test(arr):
    length = len(arr)
    if length<=1:
        return arr
    res = []
    for i in range(length):
        temp = list.copy(arr)
        del(temp[i])
        res += [arr[i]+j for j in test(temp)]
    return res

print(test([‘a‘,‘b‘,‘c‘,‘d‘]))

　　result：

G:\python\study>python hello.py
[‘abcd‘, ‘abdc‘, ‘acbd‘, ‘acdb‘, ‘adbc‘, ‘adcb‘, ‘bacd‘, ‘badc‘, ‘bcad‘, ‘bcda‘, ‘bdac‘, ‘bdca‘, ‘cabd‘, ‘cadb‘, ‘cbad‘, ‘cbda‘, ‘cdab‘, ‘cdba‘, ‘dabc‘, ‘dacb‘, ‘dbac‘, ‘dbca‘, ‘dcab‘, ‘dcba‘]

输出k个的排列组合，k不大于字符串长度 n!/(n-k)!

def test(arr,k):
    length = len(arr)
    if k<=1:
        return arr
    res = []
    for i in range(length):
        temp = list.copy(arr)
        del(temp[i])
        res += [arr[i]+j for j in test(temp,k-1)]
    return res

print(test([‘a‘,‘b‘,‘c‘,‘d‘],2))

　　result:

G:\python\study>python hello.py
[‘ab‘, ‘ac‘, ‘ad‘, ‘ba‘, ‘bc‘, ‘bd‘, ‘ca‘, ‘cb‘, ‘cd‘, ‘da‘, ‘db‘, ‘dc‘]