Weaving Numbers In Python

Question

I am trying to write a code which returns a list of all possible woven numbers from two user inputted numbers. For Example,

if A = 27 and B = 54 then there are four numbers that can be woven

2574

5247

7425

4752

Weaving a number can be done by weaving from the beginning, starting with A, weaving from the beginning, starting with B, weaving from the end, starting with A, weaving from the end, starting with B. While weaving two numbers A and B, if all the digits of A are weaved and some more digits are there in B, the remaining digits of B are just appended at the end.

I am trying

num_a = input()
num_b = input()
weaved_nums = []

def permutations(string):
    if len(string) == 1:
        return string

    recursive_perms = []
    for c in string:
        for perm in permutations(string.replace(c,'',1)):
            recursive_perms.append(c+perm)

    return set(recursive_perms)

num_a_perms = list(permutations(num_a))
num_b_perms = list(permutations(num_b))

def weave(num_1, num_2):
    new_string = ''
    for i in range(len(min([num_1, num_2], key = len))):
        new_string += num_1[i] + num_2[i]
    new_string += max(num_1, num_2, key=len)[len(num_1):]
    weaved_nums.append(new_string)

for i in range(len(num_a_perms)):
    for k in range(len(num_b_perms)):
        weave(num_a_perms[i], num_b_perms[k])
        weave(num_b_perms[k], num_a_perms[i])
        

print(weaved_nums)

However my program returns

['2475', '4257', '2574', '5247', '7425', '4752', '7524', '5742']

for inputs 27 and 54

When you stepped through the program or printed stuff at different places can you see where it is going wrong? Have you tested your two functions with known inputs and verified that they work? — wwii, Nov 28 '20 at 16:26
If you are using an IDE **now** is a good time to learn its debugging features - like stepping through execution, setting breakpoints, and examining values. Or you could spend a little time and get familiar with the built-in [Python debugger](https://docs.python.org/3/library/pdb.html). Also, printing *stuff* at strategic points in your program can help you trace what is or isn't happening. [What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems) — wwii, Nov 28 '20 at 16:26
I should only get the 4 numbers , 2574, 5247, 7425 and 4752 as the final list — RISHABH AGRAWAL, Nov 28 '20 at 16:26

wwii · Accepted Answer · 2020-11-28T17:13:15.247

Another solution - limited to two inputs:

start at the beginning r first: zip(r,s)
start at the end r first: zip(r[::-1],s[::-1])
start at the beginning s first: zip(s,r)
start at the end s first: zip(s[::-1],r[::-1])

def f(r,s):
    combos = ((r,s),(r[::-1],s[::-1]),(s,r),(s[::-1],r[::-1]))
    for combo in combos:
        yield ''.join(c for x,y in zip(*combo) for c in (x,y))

for thing in f('27','54'):
    print(thing)

For strings of unequal length use itertools.zip_longest(*combo,fillvalue='') instead of zip.

def f(r,s):
    combos = ((r,s),
              (r[::-1],s[::-1]),
              (s,r),
              (s[::-1],r[::-1]))

    for combo in combos:
        yield ''.join(c for x,y in itertools.zip_longest(*combo,fillvalue='') for c in (x,y))

>>> for thing in f('27','543'):
        print(thing)
25743
73245
52473
37425

score 0 · Answer 2 · answered Nov 28 '20 at 16:40

num_a = input("Enter first term:")
num_b = input("Enter second term:")
weaved_nums = []


def weave(num_1, num_2):
    new_string = ''
    for i in range(min(len(num_1), len(num_2))):
        new_string += num_1[i] + num_2[i]
    new_string += max(num_1, num_2, key=len)[min(len(num_1), len(num_2)):]
    weaved_nums.append(int(new_string))


weave(num_a, num_b)
weave(num_b, num_a)
weave(num_a[::-1], num_b[::-1])
weave(num_b[::-1], num_a[::-1])
print(max(list(map(int, weaved_nums))))

This Solution Works

Weaving Numbers In Python

2 Answers2