全排列的一种实现

全排列的一个实现。

import math

def per( seq ):
    count = len( seq )
    resCount = math.factorial( count )
    ress = [ ['']*count for i in range(resCount) ]

    for i in range(count):
        base = math.factorial( count-1-i )
        for index in range(resCount):
            newseq = [ x for x in seq if x not in ress[index] ]
            ssi = (index // base) % len(newseq)
            ress[index][i] = newseq[ssi]
        
    return ress

def test():
    ress = per( 'abcd' ) 
    #ress = per( 'abcde' )                                                                                               
    #ress = per('123456789')
    for res in ress:
        for x in res:
            print( x, end='' )
        print()

if __name__ == "__main__":
    test()