Python：遍历列表

Question

I´ve a mind challenge riddle that i want to resolve using python. They give 4 numbers (25, 28, 38, 35) and they want us to place the numbers in ...+...-...=... One possible solution is 25+38-35=28. I´ve tried to, making a list from the numbers, iterate them with some loops and an if: lst=[25, 28, 38, 35]

for z in lst:
    for x in lst:
        for c in lst:
            for v in lst:
                 if z+x-c==v:
                     print z,x,c,v

But when a run the for loops they repeat the numbers, (25+25-25=25) and that don´t work. How can i solve it?

Answer 1

As Luis' comment hinted, a good approach is

import itertools

for z, x, c, v in itertools.permutations(lst):
    if z+x-c==v:
        print z,x,c,v

"flat is better than nested", as import this at an interactive Python prompt will remind you:-)

Answer 2

Def recadd(lis):
       If lis[0] + lis[1] - lis[2]] = lis[3]:
                return lis
       Else: 
               recadd(lis[3] + lis[0:2])
               recadd(lis[0] + lis[3] + lis[1:2])
               recadd(lis[0:1] + lis[3]. + lis[2])

Quick and dirty hack on my mobile, could be elegantly expanded for k numbers, untested but it should work.

Edit: realized this won't work if there is no solution.infinite recursion...