有四個數字：1、2、3、4，能組成多少個互不相同且無重復數字的三位數？各是多少？

把數字變成字符再把字符拼起來：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
x = 0
for i in range(1,5):
    for j in range(1,5): 
        for k in range(1,5):
            if( i!= j)and (i != k) and (j != k):
               num  = ‘‘.join(map(str,[i,j,k]))
               x += 1
               print
 
 ‘第‘+str(x)+‘個數是：‘+num
print ‘共有‘+str(x)+‘個數滿足條件。‘

神奇的位運算：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# coding:utf-8
#從 00 01 10  到  11 10 01
for num in range(6,58):
    a = num >> 4 & 3    
    b = num >> 2 & 3    
    c = num & 3         
    if( (a^b) and (b^c) and (c^a) ):#異或
        print
 
 a+1,b+1,c+1

num = 6　　000110
000000 & 000011 = 000000   0
000001 & 000011 = 000001   1
000110 & 000011 = 000010   2
000001:1 000011:3 000010:2  
True 
1，2，3

num = 7   000111
000000 & 000011 = 000000    0
000001 & 000011 = 000001    1
000111 & 000011 = 000011    3
000001:1 000010:2 000011:3
True
1,2,4

Python狂練-1