48
\$\begingroup\$

Here is a relatively simple challenge for you.

Given a string of length N, output the string forwards, then backwards, then forwards, then backwards... etc. N times. For example, if your input was

Hello!

You should output:

Hello!!olleHHello!!olleHHello!!olleH

You may also optionally output one trailing newline.

Your submission may be either a full program or a function, and you may take input and output in any reasonable format. For example, you may take IO from STDIN/STDOUT, function arguments and return value, from a file, etc. You can safely assume that the input string will not be empty, and will only contain printable ASCII. You must output the new string on a single line. So, for example, if the output to the last example was

Hello!
!olleH
Hello!
!olleH
Hello!
!olleH

This would not be a valid solution!

Here are some more test cases:

Input:
a
Output:
a

Input:
abcd
Output:
abcddcbaabcddcba

Input:
OK!
Output:
OK!!KOOK!

Input:
4815162342
Output:
4815162342243261518448151623422432615184481516234224326151844815162342243261518448151623422432615184

Input:
PPCG
Output:
PPCGGCPPPPCGGCPP

Input:
42
Output:
4224

Leaderboards

Since this is a challenge, standard loopholes are banned, and the shortest answer in bytes wins! However, this is also a competition to have the shortest answer in any particular langauge. While it's unlikely that a Java answer will beat an answer in perl, or some golfing language, it's still very impressive to have the shortest Java answer. So, you can use this leaderboard to see both

  1. The shortest answer out of all languages, and

  2. The shortest answer in each individual language.

To make sure that your answer shows up, please start your answer with a headline, using the following Markdown template:

# Language Name, N bytes

where N is the size of your submission. If you improve your score, you can keep old scores in the headline, by striking them through. For instance:

# Ruby, <s>104</s> <s>101</s> 96 bytes

If there you want to include multiple numbers in your header (e.g. because your score is the sum of two files or you want to list interpreter flag penalties separately), make sure that the actual score is the last number in the header:

# Perl, 43 + 2 (-p flag) = 45 bytes

You can also make the language name a link which will then show up in the leaderboard snippet:

# [><>](http://esolangs.org/wiki/Fish), 121 bytes

var QUESTION_ID=93261,OVERRIDE_USER=31716;function answersUrl(e){return"https://api.stackexchange.com/2.2/questions/"+QUESTION_ID+"/answers?page="+e+"&pagesize=100&order=desc&sort=creation&site=codegolf&filter="+ANSWER_FILTER}function commentUrl(e,s){return"https://api.stackexchange.com/2.2/answers/"+s.join(";")+"/comments?page="+e+"&pagesize=100&order=desc&sort=creation&site=codegolf&filter="+COMMENT_FILTER}function getAnswers(){jQuery.ajax({url:answersUrl(answer_page++),method:"get",dataType:"jsonp",crossDomain:!0,success:function(e){answers.push.apply(answers,e.items),answers_hash=[],answer_ids=[],e.items.forEach(function(e){e.comments=[];var s=+e.share_link.match(/\d+/);answer_ids.push(s),answers_hash[s]=e}),e.has_more||(more_answers=!1),comment_page=1,getComments()}})}function getComments(){jQuery.ajax({url:commentUrl(comment_page++,answer_ids),method:"get",dataType:"jsonp",crossDomain:!0,success:function(e){e.items.forEach(function(e){e.owner.user_id===OVERRIDE_USER&&answers_hash[e.post_id].comments.push(e)}),e.has_more?getComments():more_answers?getAnswers():process()}})}function getAuthorName(e){return e.owner.display_name}function process(){var e=[];answers.forEach(function(s){var r=s.body;s.comments.forEach(function(e){OVERRIDE_REG.test(e.body)&&(r="<h1>"+e.body.replace(OVERRIDE_REG,"")+"</h1>")});var a=r.match(SCORE_REG);a&&e.push({user:getAuthorName(s),size:+a[2],language:a[1],link:s.share_link})}),e.sort(function(e,s){var r=e.size,a=s.size;return r-a});var s={},r=1,a=null,n=1;e.forEach(function(e){e.size!=a&&(n=r),a=e.size,++r;var t=jQuery("#answer-template").html();t=t.replace("{{PLACE}}",n+".").replace("{{NAME}}",e.user).replace("{{LANGUAGE}}",e.language).replace("{{SIZE}}",e.size).replace("{{LINK}}",e.link),t=jQuery(t),jQuery("#answers").append(t);var o=e.language;/<a/.test(o)&&(o=jQuery(o).text()),s[o]=s[o]||{lang:e.language,user:e.user,size:e.size,link:e.link}});var t=[];for(var o in s)s.hasOwnProperty(o)&&t.push(s[o]);t.sort(function(e,s){return e.lang>s.lang?1:e.lang<s.lang?-1:0});for(var c=0;c<t.length;++c){var i=jQuery("#language-template").html(),o=t[c];i=i.replace("{{LANGUAGE}}",o.lang).replace("{{NAME}}",o.user).replace("{{SIZE}}",o.size).replace("{{LINK}}",o.link),i=jQuery(i),jQuery("#languages").append(i)}}var ANSWER_FILTER="!t)IWYnsLAZle2tQ3KqrVveCRJfxcRLe",COMMENT_FILTER="!)Q2B_A2kjfAiU78X(md6BoYk",answers=[],answers_hash,answer_ids,answer_page=1,more_answers=!0,comment_page;getAnswers();var SCORE_REG=/<h\d>\s*([^\n,]*[^\s,]),.*?(\d+)(?=[^\n\d<>]*(?:<(?:s>[^\n<>]*<\/s>|[^\n<>]+>)[^\n\d<>]*)*<\/h\d>)/,OVERRIDE_REG=/^Override\s*header:\s*/i;
body{text-align:left!important}#answer-list,#language-list{padding:10px;width:290px;float:left}table thead{font-weight:700}table td{padding:5px}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <link rel="stylesheet" type="text/css" href="//cdn.sstatic.net/codegolf/all.css?v=83c949450c8b"> <div id="answer-list"> <h2>Leaderboard</h2> <table class="answer-list"> <thead> <tr><td></td><td>Author</td><td>Language</td><td>Size</td></tr></thead> <tbody id="answers"> </tbody> </table> </div><div id="language-list"> <h2>Winners by Language</h2> <table class="language-list"> <thead> <tr><td>Language</td><td>User</td><td>Score</td></tr></thead> <tbody id="languages"> </tbody> </table> </div><table style="display: none"> <tbody id="answer-template"> <tr><td>{{PLACE}}</td><td>{{NAME}}</td><td>{{LANGUAGE}}</td><td>{{SIZE}}</td><td><a href="{{LINK}}">Link</a></td></tr></tbody> </table> <table style="display: none"> <tbody id="language-template"> <tr><td>{{LANGUAGE}}</td><td>{{NAME}}</td><td>{{SIZE}}</td><td><a href="{{LINK}}">Link</a></td></tr></tbody> </table>

\$\endgroup\$
9
  • \$\begingroup\$ In your example, shouldn't that be olleH, not elloH ? \$\endgroup\$
    – Arnaud
    Sep 15 '16 at 3:27
  • 2
    \$\begingroup\$ @Downgoat No, you must take input and output in the same format as the spec describes. \$\endgroup\$
    – DJMcMayhem
    Sep 15 '16 at 4:15
  • 4
    \$\begingroup\$ Shouldn't the title be StringgnirtSStringgnirtSStringgnirtS? \$\endgroup\$
    – Luis Mendo
    Sep 15 '16 at 8:39
  • 2
    \$\begingroup\$ @carusocomputing It won't: "You can safely assume that the input string will not be empty, and will only contain printable ASCII." \$\endgroup\$ Sep 15 '16 at 13:50
  • 1
    \$\begingroup\$ en.wikipedia.org/wiki/ASCII#Printable_characters Ah, didn't know that was a well defined subset of ASCII. I imagined printable to include \t, \n, etc... \$\endgroup\$ Sep 15 '16 at 14:59

94 Answers 94

1 2 3
4
0
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Burlesque, 15 bytes

saS[jJ<-_+cyj.+

Try it online!

sa  # Length of input
S[  # Squared
jJ  # Duplicate the input
<-  # Reverse it
_+  # Join them
cy  # Repeat infinitely
j.+ # Take the first length-squared characters
\$\endgroup\$
0
\$\begingroup\$

C++ (gcc), 112 bytes

#import<bits/stdc++.h>
int f(std::string&s){for(int x=s.length();x--;std::reverse(&s[0],&*end(s)))std::cout<<s;}

Requires a non-const, mutable std::string. It reverses the string after every iteration and prints it.

-3 bytes thanks to ceilingcat!

Try it online!

\$\endgroup\$
1
  • \$\begingroup\$ @ceilingcat Thank you! Incorporated. \$\endgroup\$
    – S.S. Anne
    Feb 4 '20 at 23:55
0
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Ly, 23 bytes

&iysp>l[<&s&o&lr&s>1-]p

Try it online!

At a high level, the code stores the input string in the "backup cell" restoring it, printing, reversing and re-saving each time through the loop. The loop counter is in a separate stack.

&iysp>l[<&s&o&lr&s>1-]p #
&i                      # Read the input onto the stack (as codepoints)
  ysp                   # Get the length, stash in the backup cell, pop from stack
     >l                 # Switch stacks, load the input lenght (loop counter)
        [         >1-]  # Loop, switch to loop counter stack, and decrement
         <&s            # Switch to the output stack, restore string from backup cell
           &o           # Print the stack
             &lr&s      # Restore string again, reverse stack and re-save
                      p # Delete loop counter to prevent it from printing
\$\endgroup\$
-1
\$\begingroup\$

C++ (gcc), 91 bytes

void f(string s){ for(int i = 0; i++ < s.size(); reverse(s.begin(), s.end())) cout << s;  }

Try it online!

\$\endgroup\$
1
  • 2
    \$\begingroup\$ You could remove those abundant whitespace... But how are you able to use string functions and cout without including them in your code? \$\endgroup\$
    – user85052
    Dec 4 '19 at 13:36
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