সংখ্যার বিপরীততমতমতম উপায়

Question

একটি একক পূর্ণসংখ্যার মূল্যবান আর্গুমেন্ট গ্রহণ করার জন্য একটি ফাংশন (বা সমমানের সাবপ্রগ্রাম) লিখুন এবং যুক্তির বেস -10 ডিজিটের ক্রমকে বিপরীত করে পাওয়া (একই ধরণের টাইপযুক্ত) মানটি ফিরিয়ে দিন।

উদাহরণস্বরূপ 76543 34567 প্রদান করুন

Comments

Go back to the time the number was a string, then reverse the string

— pmg

The idea of a "shortest algorithm" is somewhat specious, especially if you'll allow "any language." Think up an algorithm, and I'll give you a DSL with an appropriate "~" operator ...

Just a notice: any number ending with 0 becomes a shorter number of digits when reversed...

— powtac

I know an algorithm that takes no time at all, but only works on palindromic numbers ;)

— schnaader

Found time to do the re-write myself. I hope this remain the puzzle that eltond meant to pose.

— dmckee

Answer 1

HTML 21 7 chars (1 char if I'm cheeky...)

‮n

replace n with your number

Comments

This is just plain genius. I'd go for one char. Or 2, as it encodes to two bytes in UTF-16 :P

— tomsmeding

Hahaha I did a Google search on that tag and was rewarded with Your search -‮ - did not match any documents.

— JoeFish

U could try this link in browser: data:text/html,&%238238;egnahcxEkcatS olleH

— F. Hauri

Funny in google transate too. @JoeFish: I can't reproduce, please post a link! ‮

— F. Hauri

@JoeFish When I look at the comment, your username is flipped and there is some text after it. ‮txet emos si ereH

— Stefnotch

Answer 2

Python

int(str(76543)[::-1])

EDIT:

Shorter solution as suggested by @gnibbler:

int(`76543`[::-1])

or, if above is unclear:

x=76543
int(`x`[::-1])

Comments

s[::-1] is a lot faster than ''.join(reversed(s))

— riza

You can use backticks (for repr) instead of using str

— gnibbler

@gnibbler Thanks for suggestion. I've updated my answer.

— Vader

TBH, that ain't a function/proceduce/whatever you want to call it, and the specs require it.

— Thomas Eding

Also, it doesn't even accept a value...

— Exelian

Answer 3

Universal (language agnostic/independent)

If you want to use only numbers (avoid converting the number to string) and don't want to use some specific library (to be universal for any language):

x = 76543 # or whatever is your number
y = 0
while x > 0:
    y *= 10
    y += ( x %10 )
    x /= 10 # int division 

_{This is python, but it could be done in any language, because it's just a math method.}

Comments

If you replace mod with %, it's valid Python ;)

— phihag

You're right, actually :) 10x

Not the shortest, but the most common and universal.

— Kiril Kirov

y=y*10+x%10....

— st0le

BrainFuck doesn't, though it can be calculated. Any language that doesn't have it can use a - (n * int(a/n)) instead of a mod n. Also, if you look here, the modulus operation is implemented differently in every language. (See the table on the right.)

— mbomb007

Answer 4

Perl 6

+$n.flip

or:

$n.flip

for dynamically typed code.

Numbers got string methods due to language design.

Answer 5

J - 6 characters + variable

".|.":y

Where y is your value.

Comments

As a function: |.&.": "reverse under do" which is pretty much a literal translation of the task.

— FireFly

Answer 6

APL (3)

⍎⌽⍕

Usage:

⍎⌽⍕12345 => 54321

Answer 7

PHP, 9 chars

(int)strrev(123);

To do it short where N is a constant:

strrev(N)

Answer 8

Befunge (3 characters)

Complete runnable program:

N.@

Where N is your number. Rules say "accept a single integer valued argument"; In Befunge you can only enter integers from 0 to 9.

Comments

Those are the only literals, but other numbers could certainly be represented. Otherwise, the winning answer would be Brainfuck with the empty program. ;-)

— FireFly

Answer 9

Language-independent/mathematics

Inspired by Kiril Kirov's answer above. I got curious about the mathematical properties of reversing a number, so I decided to investigate a bit.

Turns out if you plot the difference n - rev(n) for natural numbers n in some base r, you get patterns like this ((n - rev(n)) / (r - 1), for r=10, wrapped at r columns, red denotes negative number):

This sequence could be generated as such (pseudocode):

for i=1 to r:
  output 0

for m=0, 1, …
  for k=1 to (r-1):
    for d=1 to r^m:
      for i=0 to (r-1):
        output (r-1) * (r+1)^m * (k - i)

If you store these values in a list/array, then n - arr[n] would get you the reversed form of n. Now, to "mathematically golf" this, we'd ideally want a closed-form expression that gives us the n:th value in the sequence, so that we could have a closed-form expression for solving the entire task. Unfortunately, I haven't been able to find such an expression... but it looks like it should be possible. :(

So yeah, not so much a code-golf as a mathematical curiosity, but if there is a closed-form expression of the above sequence it might actually be useful in proper PL golf submissions.

Answer 10

Haskell, 28 24 characters

f=read.reverse.show.(+0)

Comments

How about f=read.reverse.show.(+0)?

— FUZxxl

(+0): Legit man! Though technically you don't need the .(+0) at all, as f would be more polymorphic than what the problem requires (it is allowed to return a 'similarly typed' output). I would shave off those 5 characters.

— Thomas Eding

Answer 11

Vim

17 chars

:se ri<CR>C<C-R>"

Comments

I would say that's 10 chars (keystrokes) if you type the command directly in vim. Btw, I learned something new in vim today, thanks :)

— daniero

Answer 12

Scala - 33 Chars

def r(a:Int)=(a+"").reverse.toInt

Comments

+1 for scala, nice to see something else than python/ruby/perl

— lhk

This will fail on negative Int. -123 should return -321

— samach

Answer 13

Ruby (14)

x = 13456
x.to_s.reverse

Comments

"no" is undefined. I think you meant to put "x" there.

— David Rivers

123456.to_s.reverse is even shorter.

— Steffen Roller

@mmdemirbas - thanks for fixing the typo

— bodacious

Needs to be .to_s.reverse.to_i to comply with spec.

— histocrat

A number that starts with 0 doesnt seem to work. 0112.to_s.reverse.to_i => 47

— Joel

Answer 14

It is possible to convert a number a string, then reverse the string and then convert that string back to number. This kind of feature is probably available in all language. If you are looking for a more mathematical method then this might help:

int n = 76543;
int r = 0;

while (n > 0) {
    r *= 10;
    r += n % 10;
    n /= 10;
}

Comments

Mine is absolutely the same (:

Ya, only difference is your code looks like Python.

This method overflow's on languages with limited precision. try 1111111119

— st0le

Answer 15

Python 3+

Function form: 28 characters

r=lambda i:int(str(i)[::-1])

(Sub)program form: 25 characters

print(input()[::-1])

I consider some of the other Python examples to be cheating, or at least cheap, due to using hardcoded input and/or not fully satisfying the requirements.

Answer 16

Golfscript, 5 chars

`-1%~

This takes an argument on the stack and leaves the result on the stack. I'm exploiting the "subprogram" option in the spec: if you insist on a function, that's four chars more leaving it on the stack:

{`-1%~}:r

Comments

I think you must've meant `-1%~ rather than `-1$~ (and I've taken the liberty of editing your answer to say so).

— Ilmari Karonen

Answer 17

In shell scripting :

  echo "your number"|rev

Hope this was useful :)

Comments

good one! didn't know bash was capable to that also!

— Pranit Bauva

I guess technically it does return a similarly-typed "number"... could be shortened further with rev<<<yournumber, e.g. rev<<<132 (for bash/zsh, not per POSIX though)

— FireFly

Just rev is enough, the question doesn't say it has to be a function. You could compare rev to a built-in function, even though it's not one.

— nyuszika7h

this is invalid: 'rev' is not a builtin, but an external program call.

— Bastian Bittorf

67 Bytes pure POSIX shell: X=$1;while [ $X != 0 ];do Y=$((Y*10+X%10));X=$((X/10));done;echo $Y

— Bastian Bittorf

Answer 18

Kinda late but

APL, 3

⍎⌽⍞

If you insists on a function

⍎∘⌽∘⍕

Comments

Well looks like I couldn't spot a duplicate above...(due to it being on the 2nd page)

— TwiNight

I'm sad, that nobody gave brainfu*k or whitespace solution :( (one more vote and you're on the first page )

— Kiril Kirov

@KirilKirov I've a brainfu*k solution : codegolf.stackexchange.com/a/32826/24829

— rpax

Answer 19

Mathematica, 14 bytes

IntegerReverse

This is not competing, because this function was only added in last week's 10.3 release, but for completeness I thought I'd add the only ever (I think?) built-in for this task.

Answer 20

You could do the following in Java. Note that this converts to String and back and is not a mathematical solution.

public class test {
    public static int reverseInt(int i) {
        return Integer.valueOf((new StringBuffer(String.valueOf(i))).reverse().toString());
    }

    public static void main(String[] args) {
        int i = 1234;
        System.out.println("reverse("+i+") -> " + reverseInt(i));
    }
}

Comments

It is a mathematical solution. Mathematics is not numbers is not arithmetics. Mathematics also deals with strings of symbols. And in this special case, the conversion to and from string is just conversion to and from base-10.

— R. Martinho Fernandes

What I meant by "not a mathematical solution" is that we're not doing any math ourselves. The methods are doing all of the parsing and mathematics for us. As opposed to e.g. Kiril Kirov's answer.

— Victor

Will Overflow...

— st0le

Answer 21

Lua

Numbers and strings are interchangeable, so this is trivial

string.reverse(12345)

Answer 22

This one ACTUALLY takes an input, unlike some of the rest:

print`input()`[::-1]

Python btw.

Answer 23

Actionscript

43 characters. num as the parameter to the function:

num.toString().split('').reverse().join('')

Answer 24

Groovy

r={"$it".reverse() as BigDecimal}

assert r(1234) == 4321
assert r(345678987654567898765) == 567898765456789876543
assert r(345346457.24654654) == 45645642.754643543

Answer 25

Perl, 11 chars

The p flag is needed for this to work, included in the count.

Usage:

$ echo 76543 | perl -pE '$_=reverse'

Comments

I count 10 chars

— F. Hauri

The p flag is included in the count

— Zaid

Answer 26

Clojure (42 chars)

#(->> % str reverse(apply str)read-string)

Example usage:

(#(->> % str reverse(apply str)read-string) 98321)

returns 12389

Answer 27

Common Lisp - 60 chars

(first(list(parse-integer(reverse(write-to-string '4279)))))

will get you 9724.

Comments

Why (first(list? parse-integer already returns the number.

— Florian Margaine

Answer 28

K, 3 bytes:

.|$

Evaluate (.) the reverse (|) of casting to a string ($).

Usage example:

  .|$76543
34567

Answer 29

rs, 20 bytes

#
+#(.*)(.)/\2#\1
#/

Technically, this doesn't count (rs was created earlier this year), but I didn't see any other regex-based answers, and I thought this was neat.

Live demo.

Explanation:

#

Insert a pound character at the beginning of the string. This is used as a marker.

+#(.*)(.)/\2#\1

Continuously prepend the last character of the main string to the area before the marker until there are no characters left.

#/

Remove the marker.

Answer 30

mIRC 4.45 (35 Bytes)

$regsubex(12,/(.)/g,$mid(\A,-\n,1))