Let's do the Wave!

Question

Input:

• A string (the wave-snippet) with a length >= 2.
• A positive integer n >= 1.

Output:

We output a single-line wave. We do this by repeating the input string n times.

Challenge rules:

• If the first and last character of the input string matches, we only output it once in the total output (i.e. ^_^ of length 2 becomes ^_^_^ and not ^_^^_^).
• The input string won't contain any whitespaces/tabs/new-lines/etc.
• If your language doesn't support non-ASCII characters, then that's fine. As long as it still complies to the challenge with ASCII-only wave-input.

General rules:

• This is code-golf, so shortest answer in bytes wins.
  Don't let code-golf languages discourage you from posting answers with non-codegolfing languages. Try to come up with an as short as possible answer for 'any' programming language.
• Standard rules apply for your answer, so you are allowed to use STDIN/STDOUT, functions/method with the proper parameters, full programs. Your call.
• Default Loopholes are forbidden.
• If possible, please add a link with a test for your code.
• Also, please add an explanation if necessary.

Test cases:

_.~"(              length 12
_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(

'°º¤o,¸¸,o¤º°'     length 3
'°º¤o,¸¸,o¤º°'°º¤o,¸¸,o¤º°'°º¤o,¸¸,o¤º°'

-__                length 1
-__

-__                length 8
-__-__-__-__-__-__-__-__

-__-               length 8
-__-__-__-__-__-__-__-__-

¯`·.¸¸.·´¯         length 24
¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯

**                 length 6
*******

String & length of your own choice (be creative!)

Answer 1

Python 3, 32 bytes

lambda s,n:s+s[s[0]==s[-1]:]*~-n

Concatenates n copies of the string, removing the first character from all copies but the first if the first character matches the last one.

Answer 2

05AB1E, 13 bytes

Uses CP-1252 encoding.

D¬U¤XQi¦}I<×J

Try it online!

Explanation

-___- and 3 used as input for example.

D              # duplicate input string
               # STACK: "-___-", "-___-"
 ¬U¤X          # push copies of the first and last element of the string
               # STACK: "-___-", "-___-", "-", "-"
     Q         # compare for equality 
               # STACK: "-___-", "-___-", 1
      i¦}      # if true, remove the first char of the copy of the input string
               # STACK: "-___-", "___-" 
         I<    # push input number and decrease by 1
               # STACK: "-___-", "___-", 2
           ×   # repeat the top string this many times
               # STACK: "-___-", "___-___-"
            J  # join with input string
               # STACK: "-___-___-___-"
               # implicitly output

Answer 3

JavaScript (ES6), 47 bytes

f=
(s,n)=>s+s.slice(s[0]==s.slice(-1)).repeat(n-1)
;

<div oninput=o.textContent=n.value&&f(s.value,n.value)><input id=s><input id=n type=number min=1><div id=o>

Answer 4

Pyke, 15 14 10 bytes

tQQhQeq>*+

Try it here!

  QhQeq    -    input_1[0] == input_1[-1]
 Q     >   -   input_1[^:]
        *  -  ^ * V
t          -   input_2 - 1
         + - input_1 + ^

Answer 5

Perl, 29 bytes

28 bytes code + 1 for -p.

Thanks to @Dada for helping me shave off a few bytes!

s/^((.).*?)(\2?)$/$1x<>.$3/e

Usage

perl -pe 's/^((.).*?)(\2?)$/$1x<>.$3/e' <<< "'°º¤o,¸¸,o¤º°'
3"
'°º¤o,¸¸,o¤º°'°º¤o,¸¸,o¤º°'°º¤o,¸¸,o¤º°'
perl -pe 's/^((.).*?)(\2?)$/$1x<>.$3/e' <<< '**
6'
*******

Online example.

Answer 6

Perl, 23 bytes

Includes +1 for -p

Give input string followed by number on separate lines on STDIN

wave.pl <<< "'°º¤o,¸¸,o¤º°'
3"

wave.pl:

#!/usr/bin/perl -p
$_ x=<>;s/(.)\K
\1?//g

If the first character in the word is not a regex special character this 22 bytes version works too:

#!/usr/bin/perl -p
$_ x=<>;/./;s/
$&?//g

Answer 7

MATL, 19 17 14 bytes

ttP=l):&)liX"h

This works for ASCII on the online interpreter and for both unicode and ASCII when run using MATLAB.

Try it Online!

Explanation

        % Implicitly grab the input as a string
        %   STACK:  {'abcdea'}
        %
tt      % Make two copies and push them to the stack
        %   STACK:  {'abcdea'    'abcdea'    'abcdea'}
        %
P       % Flip the second copy around
        %   STACK:  {'abcdea'    'abcdea'    'aedcba'}
        %
=       % Perform an element-wise comparison. Creates a boolean array
        %   STACK:  {'abcdea'    [1 0 0 0 1]}
        %
l)      % Get the first element. If the first and last char are the same this will be
        % TRUE (1), otherwise FALSE (0)
        %   STACK:  {'abcdea'    1 }
        %
:       % Create an array from [1...previous result]. If the first char was repeated,
        % this results in the scalar 1, otherwise it results in an empty array: []
        %   STACK: {'abcdea'    1 } 
        %
&)      % Break the string into pieces using this index. If there were repeated
        % characters, this pops off the first char, otherwise it pops off
        % an empty string
        %   STACK: {'a'    'bcdea'}
        %
li      % Push the number 1 and explicitly grab the second input argument
        %   STACK: {'a'    'bcdea'    1    3}
        %
X"      % Repeat the second string this many times
        %   STACK: {'a'    'bcdeabcdeabcdea'}
        %
h       % Horizontally concatenate the first char (in case of repeat) 
        % or empty string (if no repeat) with the repeated string
        %   STACK: {'abcdeabcdeabcdea'}
        %
        % Implicitly display the result

Answer 8

Retina, 29 bytes

Lines 2 and 5 have a trailing space.

 .+
$* 
 $


 $`
(.) +\1?
$1

Try it online! (The first line enables a linefeed-separated test suite.)

Answer 9

Batch, 117 bytes

@set/ps=
@set t=%s%
@if %s:~0,1%==%s:~1% set t=%s:~1%
@for /l %%i in (2,1,%1)do @call set s=%%s%%%%t%%
@echo %s%

Takes the number of repetitions as a command-line parameter and reads the string from STDIN.

Answer 10

Pyth, 13 bytes

+z*@tBzqhzezt

Test suite!

Explanation to follow.

Answer 11

Gema, 41 characters

* *=@subst{\? \$1=\?\; =;@repeat{$2;$1 }}

Sample run:

bash-4.3$ gema '* *=@subst{\? \$1=\?\; =;@repeat{$2;$1 }}' <<< '_.~"( 12'
_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(

bash-4.3$ gema '* *=@subst{\? \$1=\?\; =;@repeat{$2;$1 }}' <<< "'°º¤o,¸¸,o¤º°' 3"
'°º¤o,¸¸,o¤º°'°º¤o,¸¸,o¤º°'°º¤o,¸¸,o¤º°'

bash-4.3$ gema '* *=@subst{\? \$1=\?\; =;@repeat{$2;$1 }}' <<< '** 6'
*******

Answer 12

PowerShell v2+, 48 bytes

Param($s,$n)$s+$s.Substring($s[0]-eq$s[-1])*--$n

Outputs the whole string once, followed by n-1 copies of the string or substring, depending on if the first and last characters match.

The .Substring() method outputs from the index supplied to the end of the string, so if $s[0]-eq$s[-1] evaluates to false (0), we get the whole string. If that statement is true (1), We get the substring starting at the second character.

Answer 13

VBA 119 bytes

New to this game and vba wins with the highest bytes :P

PS: can't believe vba stands close to JAVA HAHA

Function l(s,x)
l=s: s=IIf(Left(s,1)=Right(s,1),Mid(s,2,Len(s)),s)
z: x=x-1: If x>0 Then l=l & s: GoTo z:
End Function

Explanation:

+------------------------------------------------------------+-----------------------------------------------------------------------------------+
|                            code                            |                                     function                                      |
+------------------------------------------------------------+-----------------------------------------------------------------------------------+
| l=s                                                        | input string s is saved to base                                                   |
| s = IIf(Left(s, 1) = Right(s, 1), Right(s, Len(s) - 1), s) | checks whether 1 and last char is equal,                                          |
|                                                            | if yes removes the first char from s and that s will be used to for further joins |
| z:                                                         | z: is a label                                                                     |
| x = x - 1:                                                 | decreases looping round                                                           |
| If x > 0 Then l = l & s: GoTo z:                           | join strings until no more rounds to do                                           |
+------------------------------------------------------------+-----------------------------------------------------------------------------------+

Answer 14

CJam, 16 15 bytes

l]li*{(s@)@|@}*

Try it online

Explanation:

l]li*            Create a list of n-times the input string.
{(s@)@|@}*       Fold this list by taking out the last character of the first 
                 argument and the first character of the second argument and 
                 replacing them by their unique set union.
                 e.g.: "aba" "aba" -> "ab" 'a"a"| "ba" -> "ab" "a" "ba"
                       "abc" "abc" -> "ab" 'c"a"| "bc" -> "ab" "ca" "bc

Answer 15

K, 12 Bytes

{,/[y#(,)x]}


/in action
{,/[y#(,)x]}["lollol";4]
"lollollollollollollollol"
{,/[y#(,)x]}["-_";10]
"-_-_-_-_-_-_-_-_-_-_"

/explanation (read function from right to left)
x is the string and y is the number of repetitions
(,)y    --enlist x so it becomes 1 value (rather than a list)
y#x     --take y many items of x
,/      --coalesce the list ,/[("-_";"-_")] --> "-_-_"

Thanks

Answer 16

PHP, 72 Bytes

<?=($a=$argv[1]).str_repeat(substr($a,$a[0]==substr($a,-1)),$argv[2]-1);

with PHP 7.1 it could be reduce to 65 Bytes

<?=($a=$argv[1]).str_repeat(substr($a,$a[0]==$a[-1]),$argv[2]-1);

Answer 17

Pip, 18 bytes

Regex solution, taking advantage of the "no spaces in input" rule. Takes the string from stdin and the number as a command-line argument.

(q.s)XaR`(.) \1?`B

Try it online!

Explanation:

 q.s                Read from stdin and append a space
(   )Xa             String-multiply by first cmdline arg
       R            Replace
        `(.) \1?`     Regex: char followed by space followed by (optional) same char again
                 B    Callback function, short for {b}: return 1st capturing group

Thus, a b turns into ab, a a turns into a, and the space at the end of the string is removed. Then the result is autoprinted.

Answer 18

Haskell, 59 bytes

a%b=concat$replicate a b
a@(s:z)#n|s/=last z=n%a|1<2=s:n%z

Ungolfed version:

-- Helper: Appends str to itself n times
n % str = concat (replicate n str)

-- Wave creating function
(x:xs) # n
 -- If start and end of wave differ, 
 | x /= last xs = n%(x:xs)
 | otherwise   = x:(n%xs)

Answer 19

Java 11, 123 111 109 107 102 100 79 58 bytes

s->n->s+s.substring(s.matches("(.).*\\1")?1:0).repeat(n-1)

Try it online.

I'll of course try to answer my own question. ;)
-5 bytes thanks to @dpa97.
-21 bytes converting from Java 7 to 10.
-21 bytes converting from Java 10 to 11.

Explanation:

s->n->             // Method with String & integer parameters and String return-type
  s                //  Return the input-String as result
   +               //  Appended with:
    s.subtring(    //   A substring of the input-String:
      s.matches("(.).*\\1")?
                   //    If the first and last characters are the same:
       1           //     Remove the first character in the substring-call
      :            //    Else:
       0)          //     Use the input-String as is
     .repeat(n-1)  //   Repeated the input-integer minus 1 amount of times

Answer 20

Javascript ES6, 49 chars

(s,n)=>s.replace(/(.).*?(?=\1?$)/,m=>m.repeat(n))

Test:

f=(s,n)=>s.replace(/(.).*?(?=\1?$)/,m=>m.repeat(n))
console.log(document.querySelector("pre").textContent.split(`
`).map(s=>s.split` `).every(([s,n,k])=>f(s,n)==k))

<pre>_.~"( 12 _.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(
'°º¤o,¸¸,o¤º°' 3 '°º¤o,¸¸,o¤º°'°º¤o,¸¸,o¤º°'°º¤o,¸¸,o¤º°'
-__ 1 -__
-__ 8 -__-__-__-__-__-__-__-__
-__- 8 -__-__-__-__-__-__-__-__-
¯`·.¸¸.·´¯ 24 ¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯
** 6 *******</pre>

Answer 21

QBIC, 65 bytes

;:~left$$|(A,1)=right$$|(A,1)|A=left$$|(A,len(A)-1)][1,a|B=B+A]?B

I guess I should add LEFT$ and RIGHT$ to QBIC...

Explanation:

;          make the first cmd line parameter into A$
:          make the second cmd line parameter into a (num)
~left..]   Drop the last char if equal to the first char
[1,a...]   FOR the given number of repetitions, concat A$ to B$ (starts out empty)
?B         print B$

Answer 22

C#, 79 bytes

(s,n)=>s+new string('x',n-1).Replace("x",s[0]==s[s.Length-1]?s.Substring(1):s);

A bit of an absurd method of repeating a string. Create a new string of the desired repeat length and then replace each character with the string to repeat. Other than that, looks like pretty much the same strategy as many others.

/*Func<string, int, string> Lambda =*/ (s, n) =>
    s                                      // Start with s to include first char at start
    + new string('x', n - 1).Replace("x",  // Concatenate n-1 strings of...
        s[0] == s[s.Length - 1]            // if first/last char are the same
            ? s.Substring(1)               // then skip the first char for each concat
            : s                            // else concat whole string each time
    )
;

Answer 23

SpecBAS - 68 bytes

1 INPUT a$,n: l=LEN a$: ?IIF$(a$(1)<>a$(l),a$*n,a$( TO l-1)*n+a$(l))

Uses inline-IF to check if first and last characters are the same. If not, print string n number of times. Otherwise, splice the string to length-1, repeat that and put last character at end.

Can only accept ASCII characters (or characters built into SpecBAS IDE)

Answer 24

APL, 19 bytes

{⍺,∊1↓⍵⍴⊂⍺↓⍨⊃⍺=⊃⌽⍺}

Usage:

      '^_^' {⍺,∊1↓⍵⍴⊂⍺↓⍨⊃⍺=⊃⌽⍺} 5
^_^_^_^_^_^

Explanation:

• ⊃⍺=⊃⌽⍺: see if the first character matches the last character
• ⍺↓⍨: if this is the case, drop the first character
• ⊂: enclose the result
• ⍵⍴: replicate it ⍵ times
• 1↓: drop the first one (this is shorter than (⍵-1)⍴)
• ∊: get all the simple elements (undo the boxing)
• ⍺,: add one instance of the whole string to the front

Answer 25

Postscript, 98 bytes

exch/s exch def/l s length 1 sub def s 0 get s l get eq{/s s 0 l getinterval def}if{s print}repeat

...but you might need a ' flush' tacked onto that to get your PS interpreter to flush the comm buffer, another six bytes :(

Answer 26

Common Lisp (LispWorks), 176 bytes

(defun f(s pos)(if(equal(elt s 0)(elt s #1=(1-(length s))))(let((s1(subseq s 0 1))(s2(subseq s 0 #1#)))(dotimes(j pos)(format t s2))(format t s1))(dotimes(j pos)(format t s))))

Usage:

    CL-USER 130 > (f "_.~~\"(" 12)
    _.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(_.~"(
    NIL

    CL-USER 131 > (f "'°o¤o,??,o¤o°'" 3)
    '°o¤o,??,o¤o°'°o¤o,??,o¤o°'°o¤o,??,o¤o°'
    NIL

    CL-USER 132 > (f "-__" 1)
    -__
    NIL

    CL-USER 133 > (f "-__" 8)
    -__-__-__-__-__-__-__-__
    NIL

    CL-USER 134 > (f "ˉ`·.??.·′ˉ" 24)
    ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ`·.??.·′ˉ
    NIL

    CL-USER 135 > (f "**" 6)
    *******
    NIL

Explanation:

~~ =>   ~

\" =>   " 

Ungolf:

    (defun f (s pos)
      (if (equal (elt s 0) (elt s (1- (length s))))
          (let ((s1 (subseq s 0 1)) (s2 (subseq s 0 (1- (length s)))))
            (dotimes (j pos)
              (format t s2))
            (format t s1))        
        (dotimes (i pos)
          (format t s))))

Answer 27

Vim, 17 bytes

The easy way to do this is to use a back-reference regex that can tell if the first and last chars match. But long regexes are long. We don't want that.

lDg*p^v$?<C-P>$<CR>hd@aP

The wave to repeat is in the buffer. I'm assuming the number to be repeated is in the register "a (type qaNq with N as the number to set it up). The idea is:

• If the first and last bytes match, delete everything up to the last character.
• If the first and last bytes don't match, delete all the characters.

Then P the deleted text @a times.

• lDg*: This maneuver creates a regex that matches any first character, regardless of whether it needs to be escaped or not, or whether it's a word or not. (* would be enough to make the properly escaped regex, but would add unwanted \<\> garbage if it was a word character, like _.)
• p^: Last step was messy. Clean up to the original position, beginning of the line.
• v$: In visual mode, $ by default moves to after the end of the line.
• ?<C-P>$<CR>hd: If the previous regex exists at the end of the line, this search will move to it; otherwise, stay beyond the end of the line. Move left from there and we accomplish the (tedious) delete we need.
• @aP: Run the number repeat as a macro to be used as an argument to P.

Answer 28

Ruby, 38 bytes

->s,n{s[0]==s[-1]?s[0..-2]*n+s[0]:s*n}

I think this is pretty self-explanatory. I'm still wondering if there's a more concise way to represent the s[0..-2] block, but I haven't found it yet.

Answer 29

Java (117 bytes)

String w(String a,int b){String c=a;for(;b>0;b--)c+=b+a.substring(a.charAt(a.length()-1)==a.charAt(0)?1:0);return c;}