如何获得两个列表中整数和运算的所有组合？

Question

I have two lists:

ints = [10, 20, 30, 40, 50]

and

opers = ['+', '-', '*', '/']

I would like to obtain a list which has all possible combinations of these two lists such as:

10+20*40-30/50 = 810

50-40+30*20/10 = 70

etc.

The list should then be [810, 70, ...]

I believe there should be 2880 total elements in this list. If int[0]==int[1] , they'll count as separate for this purpose.

I think I'll have to use eval() two actually get the elements in the list. I just can't figure out how to permute the two lists in this way. Any help will be appreciated.

Thank you

Answer 1

The key is to use the itertools.permutations function. This is the naive way:

import itertools

ints = [10, 20, 30, 40, 50]
opers = ['+', '-', '*', '/']

for i in itertools.permutations(ints):
    for o in itertools.permutations(opers):
        s = f'{i[0]}{o[0]}{i[1]}{o[1]}{i[2]}{o[2]}{i[3]}{o[3]}{i[4]}'
        print(f'{s} = {eval(s)}')

output looks something like this (obviously you could place in a dictionary or whatever):

...
50-10/30+40*20 = 849.6666666666666
50-10/30*40+20 = 56.66666666666667
50*10+30-40/20 = 528.0
50*10+30/40-20 = 480.75
50*10-30+40/20 = 472.0
50*10-30/40+20 = 519.25
50*10/30+40-20 = 36.66666666666667
50*10/30-40+20 = -3.333333333333332
50/10+30-40*20 = -765.0
50/10+30*40-20 = 1185.0
50/10-30+40*20 = 775.0
50/10-30*40+20 = -1175.0
50/10*30+40-20 = 170.0
50/10*30-40+20 = 130.0
50+10-40*20/30 = 33.33333333333333
...

Answer 2

Create all permutations, remove those that do not fit ( number number ops ... etc) and calc:

from itertools import permutations

ints = ['10', '20', '30', '40', '50']
opers = [ '+', '-', '*', '/']


perm = permutations(ints+opers)

# sets for faster lookup    
i = set(ints)
ops = set(opers)

fil = (p for p in perm 
       if all(p[k] in i if k%2==0 else p[k] in ops 
              for k in range(len(p))))

calcMe = [''.join(f) for f in fil]

calcMe = [''.join(f) for f in fil]
for cal in calcMe:
    print(f"{cal}={eval(cal)}")
print(len(calcMe))

Output:

10+20-30*40/50=6.0
10+20-30*50/40=-7.5
10+20-30/40*50=-7.5
10+20-30/50*40=6.0
10+20-40*30/50=6.0
10+20-40*50/30=-36.66666666666667
10+20-40/30*50=-36.66666666666666
10+20-40/50*30=6.0

There are more permutations provided then needed and 'eval' in and of itself is considered "dangerous" if applied without thought. In this case it should be ok, though as I have full control over the inputs.

Answer 3

from itertools import permutations, zip_longest, chain

def all_combinations(ints, ops):
    for i in permutations(ints):
        for o in permutations(ops):
            yield "".join(filter(bool(chain.from_iterable(zip_longest(i, o)))))

The somewhat cryptic last line does the following:

For a given permutation of integers and operators, zip them (with missing values being None ). Chain those zipped pairs together, to form a sort of "combing" operation. The filter(bool, ...) call removes the None , depending on your taste there may be other ways you'd prefer. Finally, str.join turns the integer-operator sequence into a string.

Answer 4

You can create the list like this, using some itertools :

from itertools import permutations, chain, zip_longest

ints = [10, 20, 30, 40, 50]
opers = ['+', '-', '*', '/']

output = []
for int_perm in permutations(ints):
    for op_perm in permutations(opers):
        calculation = ''.join(map(str, chain.from_iterable(zip_longest(int_perm, op_perm, fillvalue=''))))
        output.append(eval(calculation))

print(len(output))
# 2880
print(output)
# [6.0, -7.5, 609.2, -25.0, -1989.3333333333333, ...]

A bit of explanation: for two given permutations of ints and opers :

(10, 30, 50, 20, 40)
('-', '*', '/', '+')

zip_longest will give us: (note that, as the opers list is shorter, the missing value will be filled by the fillvalue '' )

print(list((zip_longest(int_perm, op_perm, fillvalue=''))))
# [(10, '-'), (30, '*'), (50, '/'), (20, '+'), (40, '')]

and chaining the tuples in this list will give us:

print(list(chain.from_iterable(zip_longest(int_perm, op_perm, fillvalue=''))))
# [10, '-', 30, '*', 50, '/', 20, '+', 40, '']

We just have to map all items to strings and join them to get:

# '10-30*50/20+40'