CODEWITHSUNDEEP
pythonslice
lonesome
lonesome

Reputation: 2552

Reversing a negative number in Python

Using slice method in Python we are able to reverse strings and numbers easily. However, how could it be done when the number is negative?

def reverse(x):
    string = str(x)
    return int(string[::-1])

print(reverse(-123))

Gives an error as it returns 321-

EDIT:

Now let's have two more assumptions:

  1. If the reversed number is not within [−2^31, 2^31 − 1] it should return 0.

  2. For numbers like 120, it should return 21 as its reverse.

Now, how can we reverse -120 into -21?

Upvotes: 1

Views: 2349

Answers (3)

KnowledgeHunter Prits
KnowledgeHunter Prits

Reputation: 97

I have posted the unwrapped, simplified code to make it easier to understand the answer:

def int_reverser(test):
    if test >= 0:
        answer = int(str(test)[::-1])
    else:
        answer = -int(str(-test)[::-1])
    if -2**31 <= answer <= 2**31 - 1:
        return answer
    else:
        return 0

Upvotes: 1

Nouman
Nouman

Reputation: 7313

Edited

You can check ,if your number is negative then add - behind the output. You will get the expected output.
Therefore you code will be like:

def reverse(x):
    y = ""
    if int(x) <= -1:y="-";x = int(x)*-1
    output =  int(y+str(x)[::-1])
    if output >= -2**31 and output <= 2**31 - 1:return output
    else: return 0
    
print(reverse(-123))

Testing:

>>> reverse(-123)
-321
>>> reverse(123)
321
>>> reverse(-120)
-21
>>> reverse(120)
21
>>> reverse(123)
321
>>> reverse(-74634545484744)
0
>>> reverse(74634545484744)
0

It is also very simple and understandable.

Upvotes: 0

&#211;scar L&#243;pez
&#211;scar L&#243;pez

Reputation: 236114

Assuming that you want to preserve the sign, try this:

def reverse(x):
    ans = int(str(x)[::-1]) if x >= 0 else -int(str(-x)[::-1])
    return ans if -2**31 <= ans <= 2**31 - 1 else 0

It works as expected for all the edge cases introduced by the new requirements:

reverse(321)
=> 123
reverse(-321)
=> -123
reverse(120)
=> 21
reverse(-120)
=> -21
reverse(7463847412)
=> 2147483647
reverse(8463847412)
=> 0
reverse(-8463847412)
=> -2147483648
reverse(-9463847412)
=> 0

Upvotes: 6

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