全排列

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# 字典法
global counter
counter = 0
def gem(a, k):
    """
    k是用来表明这次递归从那个固定的数开始
    """
    n = len(a)
    global counter
    if k is n:
        print_result(a)
    else:
        for i in range(k, n):
            counter = counter+1
            a[i], a[k] = a[k], a[i]
            gem(a, k+1)
            a[k], a[i] = a[i], a[k]
def print_result(a):
    print [i for i in a]

if __name__ == '__main__':
    gem([1,2,3], 0)
    print counter

字典法生成全排列图解。