7
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This is my first time here at Code Golf SE so feel free to add your input/advice/suggestions to improve my post if necessary. The week after my computer science exam, the solutions were publicly published. One problem had a 45 line example solution but my solution was only 18 lines, (which I was very proud of), but I bet you guys here at code golf SE can do better.

Here are the requirements:

  • Takes two inputs, string1 and string2.
  • Delete the first occurrence of string2 found in the string1.
  • Add string2 in reverse order to the beginning of string1, and
  • Add string2 in reverse order to the end of the string1.
  • If string2 does not occur in string1, do not modify string1.
  • Output the modified string1

Example:

Input:

batman
bat

thebatman
bat

batman
cat

Output:

tabmantab

tabthemantab

batman

Note: The problem was intended to handle basic inputs. Assume all expected inputs are restricted to characters A-Z, numbers, or other special characters visible on your keyboard. It does not need to handle tabs or newlines.

Submissions with shortest byte counts in each language win.

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10
  • 3
    \$\begingroup\$ Can you give an example test case where string 2 doesn't occur in string 1? Also - which characters can appear in the string? Printable ASCII? Tab? Newlines? \$\endgroup\$
    – DELETE_ME
    Commented Mar 6, 2018 at 6:13
  • \$\begingroup\$ @user202729 Input "batman, robin" has output "batman" \$\endgroup\$
    – Ryan
    Commented Mar 6, 2018 at 6:17
  • \$\begingroup\$ Out of curiosity, which language did you use in the exam? \$\endgroup\$
    – DELETE_ME
    Commented Mar 6, 2018 at 6:26
  • 2
    \$\begingroup\$ And an example where string2 contains characters that are special in a regex and make naive s/string2// fail \$\endgroup\$
    – Ton Hospel
    Commented Mar 6, 2018 at 7:19
  • 2
    \$\begingroup\$ Perhaps a test case containing the second input multiple times, since we only should replace the first? Something like: "batman_and_his_bat", "bat""tabman_and_his_battab" \$\endgroup\$ Commented Mar 6, 2018 at 9:48

20 Answers 20

5
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Stax, 16 11 bytes

ÄE┘¢8·╦Ωb•∩

Run and debug it online

The corresponding ascii representation of the same program is this.

Y#xyz|eyr|Sx?

This fixes the bugs in original version. It uses conditionals and stuff.

Y                   Save 2nd input in y.  Now the two inputs are x and y.
 #                  Occurrences of y in x. (a)
  xyz               x, y, ""
     |e             replace first occurrence
       yr|S         surround with y reversed. (b)
           x        first input. (c)
            ?       a ? b : c

The result is printed implicitly.

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3
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Python, 55 bytes

lambda s,t:s.replace(t,'',1).join(2*[t[::-1]*(t in s)])

Try it online!

Using join to get the a+b+a pattern. This lets us write expression for a only once while still using a lambda. Compare:

Python 2, 57 bytes

def f(s,t):r=t[::-1]*(t in s);print r+s.replace(t,'',1)+r

Try it online!

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3
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APL (Dyalog Unicode), 36 bytesSBCS

Look ma, no regex!

Anonymous infix lambda, taking string2 as left argument and string1 as right argument. Assumes ⎕IO (Index Origin) to be 0, which is default on many systems.

{r,⍵[(⍳≢⍵)~(f⍳1)+⍳≢⍺],r←⌽⍺/⍨∨/f←⍺⍷⍵}

Try it online!

{} "dfn"; is left argument, is right argument; e.g. "bat" and "manbatmanbat":

⍺⍷⍵ find where string2 begins in string1; [0,0,0,1,0,0,0,0,0,1,0,0]

f← assign to f (find)

∨/ OR-reduction (does string2 occur at all?); 1

⍺/⍨ use that to compress string2 ("" if not found); "bat"

 reverse that; "tab"

r← assign to r (reverse)

⍵[], prepend string2 indexed by the following indices:

  ≢⍵ the length of string2; 3

   the indices of that; [0,1,2]

  ()+ add the following to that:

   f⍳1 index of first 1 in f; 3

  Now we have the indices to be removed; [3,4,5]

  ()~ the following indices except those indices:

   ≢⍵ length of string2; 12

    the indices of that; [0,1,2,3,4,5,6,7,8,9,10,11]

  Now we have the indices we want to keep; [0,1,2,6,7,8,9,10,11]

 This gives us the remaining parts of string1 followed by a reversed string2; "manmanbattab"

r, prepend r to that; "tabmanmanbattab"

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3
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C#, 148 bytes

using System.Linq;using System.Text.RegularExpressions;(a,b)=>a==(a=new Regex(Regex.Escape(b)).Replace(a,"",1))?a:(b=string.Concat(b.Reverse()))+a+b
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4
  • 2
    \$\begingroup\$ Perhaps include a tio link? (I edited your post to capitalize C# and add syntax highlighting.) \$\endgroup\$
    – Οurous
    Commented Mar 6, 2018 at 8:39
  • 2
    \$\begingroup\$ Welcome to PPCG, and nice first answer! With lambdas you are allowed to leave out the types and the trailing semi-colon, but all required imports are mandatory for the byte-count I'm afraid, so it would becomes this instead: using System.Linq;(a,b)=>a==(a=new System.Text.RegularExpressions.Regex(b).Replace(a,"",1))?a:(b=string.Concat(b.Reverse()))+a+b (128 bytes). Also, as @Ourous suggested, perhaps add a TIO link to your answer. Here is an example of how it might look like. It's unfortunate the Regex import is so long in .NET... :( \$\endgroup\$ Commented Mar 6, 2018 at 9:30
  • 1
    \$\begingroup\$ Hmm, it seems to fail for "this.is.a.test", ".". Expected output: ".thisis.a.test.", actual output: ".his.is.a.test.". Can be fixed like this: using System.Linq;using System.Text.RegularExpressions;(a,b)=>a==(a=new Regex(Regex.Escape(b)).Replace(a,"",1))?a:(b=string.Concat(b.Reverse()))+a+b (148 bytes). Try it online. \$\endgroup\$ Commented Mar 6, 2018 at 11:00
  • \$\begingroup\$ Thanks Kevin.. wow, c# is impressively unsuitable for golfing.. :) I tested my code in linqpad which I guess adds some commonly used namespaces by default. And yep, missed the need to escape it as someone pointed out in your java port of my code :) I think I am gonna use JavaScript next time. Thank you very much for taking the time. \$\endgroup\$
    – lee
    Commented Mar 6, 2018 at 11:13
3
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Ruby, 39 38 35 bytes

-3 bytes due to a neat trick by Asone Tuhid

->x,y{(x[y]&&="")?y.reverse!+x+y:x}

Try it online!

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3
  • \$\begingroup\$ 35 bytes \$\endgroup\$ Commented Mar 8, 2018 at 16:36
  • \$\begingroup\$ Wow, I was thinking for ages, how to get rid of that duplicated x[y], but didn't even know this was possible \$\endgroup\$
    – Kirill L.
    Commented Mar 8, 2018 at 17:25
  • \$\begingroup\$ It's the same idea as ||=, +=, etc. I think all a=a<op>b can be reduced to a<op>=b (or a<op>a=b in this case) if that makes sense. \$\endgroup\$ Commented Mar 8, 2018 at 17:31
2
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Python 3, 56 bytes

lambda s,t:[s,t[::-1]+s.replace(t,'',1)+t[::-1]][t in s]

Try it online!

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2
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Retina, 35 bytes

^(.*)¶(.*?)\1(.*)
¶$^$1$2$3$^$1
0A`

Try it online! $^ is new in Retina 1 and reverses its argument which is just what's needed here.

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0
2
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Java 8, 126 113 bytes

(a,b)->a.equals(a=a.replaceFirst(java.util.regex.Pattern.quote(b),""))?a:(b=new StringBuffer(b).reverse()+"")+a+b

Port of @lee's C# .NET answer, so make sure to upvote him!

Try it online.

Old 126 byte answer:

a->b->{Object r=new StringBuffer(b).reverse();return a.contains(b)?r+a.replaceFirst(java.util.regex.Pattern.quote(b),"")+r:a;}

Try it online.

Explanation:

a->b->{                    // Method with two String parameters and String return-type
  Object r=new StringBuffer(b).reverse();
                           //  2nd input reversed
  return a.contains(b)?    //  If the 1st input contains the 2nd:
    r                      //   Output the reversed 2nd input
     +a.replaceFirst(java.util.regex.Pattern.quote(b),"") 
                           //   Removed the first occurrence of the 2nd in the 1st input,
                           //   escaping any characters like dots, pluses, etc.
                           //   and then append that to the result
     +r                    //   appended with the reversed 2nd input again
   :                       //  Else:
    a;}                    //   Simply output the 1st input
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1
  • 1
    \$\begingroup\$ Fails with b = "..." ("Assume all expected inputs are restricted to characters A-Z, numbers, or other special characters visible on your keyboard." : . is a special character visible on every keyboard) \$\endgroup\$ Commented Mar 6, 2018 at 10:42
1
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Perl 5 + -pl, 38 34 bytes

$s=<>;s/\Q$s//&&s/^|$/reverse$s/ge

-4 thanks to Ton Hospel

Try it online!

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1
  • 1
    \$\begingroup\$ Good method but can be golfed a bit more: -pl $s=<>;s/$s//&&s/^|$/reverse$s/ge. Both versions really need to use s/\Q$s// though since characters like * and . seem allowed \$\endgroup\$
    – Ton Hospel
    Commented Mar 6, 2018 at 7:12
1
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05AB1E, 12 bytes

DIåiIõ.;IR.ø

Try it online!

Explanation

D             # duplicate 1st input
 Iåi          # if 2nd input is in first input
    Iõ.;      # replace the first occurrence of 2nd input with the empty string
        IR.ø  # surround with 2nd input reversed
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1
  • \$\begingroup\$ Only other thing I can think of is 13-bytes: õ.;©Ê²si®¹R.ø but it's pretty different order-wise. \$\endgroup\$ Commented Mar 6, 2018 at 15:25
1
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Javascript (ES6), 69 65 64 bytes

x=>y=>x.match(y)?(k=[...y].reverse().join``)+x.replace(y,'')+k:x

Try it online!

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4
  • 1
    \$\begingroup\$ Welcome to PPCG! / (1) In the way how we normally count byte count, the m= is not counted if you don't use it in the function (i.e., it doesn't call itself). (2) You can save a byte by currying. \$\endgroup\$
    – DELETE_ME
    Commented Mar 6, 2018 at 14:01
  • \$\begingroup\$ Also you may find Tips for golfing in Javascript useful. \$\endgroup\$
    – DELETE_ME
    Commented Mar 6, 2018 at 14:01
  • \$\begingroup\$ You can use [...y].reverse().join`` to reverse a string, save 2 bytes. \$\endgroup\$
    – DELETE_ME
    Commented Mar 6, 2018 at 14:06
  • \$\begingroup\$ Doesn't work when y contain |? \$\endgroup\$
    – l4m2
    Commented Mar 7, 2018 at 4:22
1
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K4, 36 bytes

Solution:

{$[#s:x ss y;r,(x_/(#y)#*s),r:|y;x]}

Examples:

q)k){$[#s:x ss y;r,x_/(#y)#*s,r:|y;x]}["batman";"bat"]
"tabman"
q)k){$[#s:x ss y;r,(x_/(#y)#*s),r:|y;x]}["batman";"bat"]
"tabmantab"
q)k){$[#s:x ss y;r,(x_/(#y)#*s),r:|y;x]}["thebatman";"bat"]
"tabthemantab"
q)k){$[#s:x ss y;r,(x_/(#y)#*s),r:|y;x]}["batman";"cat"]
"batman"
q)k){$[#s:x ss y;r,(x_/(#y)#*s),r:|y;x]}["batbatbat";"bat"]
"tabbatbattab

Explanation:

If string 2 (y) is found in string 1 (x) then drop first indices of first occurrence.

{$[#s:x ss y;r,(x_/(#y)#*s),r:|y;x]} / the solution
{                                  } / lambda with implicit x,y
 $[         ;                   ; ]  / $[condition;true;false]
      x ss y                         / string-search for y in x
    s:                               / save result as s
   #                                 / count length
                              |y     / reverse (|) y
                            r:       / save as r
                           ,         / join with
               (          )          / do this together
                        *s           / first (*) s
                       #             / take
                   (#y)              / length of y
                x_/                  / drop (_) over (/)
             r,                      / join with r
                                 x   / (else) return x
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1
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Jelly, 18 bytes

œṣ⁹Ḣ;jɗ⁹ṭṚ};Ṛ}ðẇ@¡

Try it online!

Full program.

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0
1
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Javascript 85 bytes

a=>b=>a.includes(b)?[...b].reverse().join``+a.replace(b,'')+[...b].reverse().join``:a

If someone knows how to avoid using split('').reverse().join('') for reversing string, please let me know

f=a=>b=>a.includes(b)?[...b].reverse().join``+a.replace(b,'')+[...b].reverse().join``:a


console.log(f('batman')('bat'))

console.log(f('thebatman')('bat'))

console.log(f('batman')('cat'))

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2
  • 1
    \$\begingroup\$ for help, you can't get much better than the Tips for golfing in javascript, and I'm sure somebody will come along to help -- I don't know javascript. \$\endgroup\$
    – Giuseppe
    Commented Mar 6, 2018 at 18:24
  • \$\begingroup\$ There's really no better way to reverse a string. What you could do is ...?(c=[...b].reverse().join``)+a.replace(b,'')+c:a to save quite a few bytes. \$\endgroup\$ Commented Mar 6, 2018 at 21:15
1
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Javascript, ES6 - 73 bytes

b=x=>y=>{v=[...y].reverse().join``;u=x.replace(y,"");alert(u==x?x:v+u+v)}
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4
  • \$\begingroup\$ please support me to improve it! \$\endgroup\$
    – NTCG
    Commented Mar 6, 2018 at 10:19
  • 1
    \$\begingroup\$ Several of the JavaScript and ES6 tips will let you shave off a number of bytes. \$\endgroup\$
    – Neil
    Commented Mar 6, 2018 at 11:03
  • \$\begingroup\$ Also, we format code blocks with 4-spaces indentation. See this. \$\endgroup\$
    – DELETE_ME
    Commented Mar 6, 2018 at 11:31
  • \$\begingroup\$ @user202729 thank you for reminding me! \$\endgroup\$
    – NTCG
    Commented Mar 7, 2018 at 3:13
0
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Python 2, 62 Bytes

def f(a,b):b*=b in a;a=a.replace(b,"",1);b=b[::-1];print b+a+b
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0
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Jelly, 21 20 bytes

œṣµḢ;j⁹$ɓ;;@ðU}
ç¹w?

Try it online!


Ouch! Why can other languages get 11~12 bytes? Am I doing something wrong?

And finally, I think I know how chain separators works...

œṣµḢ;j⁹$ɓ;;@ðU}   Helper link (dyadic). General structure:
œṣ                <dyad>                    - given x and y, split x at
                                              sublists equal to y.
   Ḣ;j⁹$                <monad>             - given x, join with y except at
                                              first index.
         ;;@                   <dyad>       - given x and y, return y+x+y.
                                              Note that this link is flipped.
             U}                      <dyad> - reverse right argument.

ç¹w?    Main link. Evaluate the last link if the second input is a substring
        of the first input, otherwise - apply identity (do nothing).
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0
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SNOBOL4 (CSNOBOL4), 73 bytes

	S =INPUT
	T =INPUT
	S T =	:F(O)
	T =REVERSE(T)
	S =T S T
O	OUTPUT =S
END

Try it online!

What's a regular expression?

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0
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AWK, 85 bytes

{for(;x++<N=split($0,a,"");)p=a[x]p;$0=NR%2?L=$0:sub($0,"",L)?p L p:L}!(NR%2)

Try it online!

Input is: primary string on odd-lines, replacement on even lines. Replacement is case sensitive.

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0
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Python 3, 58 bytes

def f(a,b):z=(b in a)*b[::-1];return z+a.replace(b,'',1)+z
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