# Interleave strings

Inspiration.* I cannot believe we have not had this challenge before:

Given one or more printable ASCII strings, interleave them by taking one character from each string, cyclically until out of characters. If a string runs out of characters before the others, just skip that one from then on.

Examples

SIMPLE gives SIMPLE

POLLS and EPEES gives PEOPLELESS

LYES and APRONS gives LAYPERSONS

ABCDE and a c and 123 567 gives Aa1B 2Cc3D E567

"\n$?* and ​ (empty string) and ,(.)"  (trailing space) gives ",\(n.$)?"*  (trailing space)

* There are shorter APL solutions.

• Since this is basically just a transpose operation, we've had a few challenges that are very similar, but possibly none that are exactly the same. – Martin Ender Dec 8 '16 at 12:10
• I had this question on my CS HW, does that mean I can close this as a homework question? ;P – Downgoat Dec 8 '16 at 14:40
• @EriktheOutgolfer Cool! I learned something today. – Adám Apr 16 '17 at 6:42

# Jelly, 1 byte

Z


Try it online!

The “transpose” built-in will do exactly this to a list of strings.

• I'm curious, what would the code have looked like if you had to pad short strings with spaces? – Adám Dec 8 '16 at 13:33
• That would be z⁶. z is “transpose left, padding with right”; ⁶ is a space. – Lynn Dec 8 '16 at 13:47
• @Adám Jelly works very well on lists; where do built-ins end and language constructs / design begin? – steenbergh Dec 8 '16 at 15:44
• @Lynn In Jelly? Anything on the Atoms and Quicks lists are buildt-ins. – Adám Dec 8 '16 at 16:08
• @Adám ;" (element-wise concatenation) would solve the task without a built-in. – Dennis Dec 8 '16 at 17:04

# Python 2, 1018986 69 bytes

I'm hoping I can get this into a lambda somehow, shortening it down by making it recursive. It isn't ideal because you would hope transposing is shorter, unfortunately it isn't (from what I have managed to come up with so far).

f=lambda s:' '*any(s)and''.join(x[:1]for x in s)+f([x[1:]for x in s])


Old solutions:

w=input();o=''
while any(w):
for i in range(len(w)):o+=w[i][:1];w[i]=w[i][1:]
print o

lambda s:''.join(''.join([c,''][c<' ']for c in x)for x in map(None,*[list(y)for y in s]))

w=input();o=''
while any(x>=' 'for x in w):
for i in range(len(w)):o+=w[i][:1];w[i]=w[i][1:]
print o

thanks to mathmandan for making me feel dumb ;) saved me a bunch of bytes! (on an old solution)

• Couldn't you just do while any(w):? Empty strings are falsey in Python. – mathmandan Dec 8 '16 at 13:30
• @mathmandan You're absolutely right, don't know what I was thinking.. – Kade Dec 8 '16 at 13:33
• No problem :) Your new solution looks great, except I think you need to prepend f=. – mathmandan Dec 8 '16 at 13:54
• You can take the [] off of the recursive call, leaving f(x[1:] for x in s), that makes it a generator comprehension, which acts the same as a list in this context. – bioweasel Aug 1 '17 at 17:37

## Perl 6, 34 32 bytes

{[~] flat roundrobin |$_».comb}  {roundrobin(|$_».comb).flat.join}


A lambda that takes an array of strings as argument, and returns a string.

• I would have used @_ instead of $_ – Brad Gilbert b2gills Dec 8 '16 at 19:13 ## CJam, 4 bytes qN/z  Try it online! We can also write an unnamed function for 4 bytes, which expects a list of strings on top of the stack: {zs}  Try it online! • That's one byte a minute! – Adám Dec 8 '16 at 12:12 # Pyth - 3 bytes Very simple, will add expansion later, on mobile. s.T  Test Suite s Join all the strings together .T Transpose, without chopping off overhang (Q implicit)  • @Daniel I'm in school too :P – Maltysen Dec 8 '16 at 14:31 • Any plans on adding the explanation? – John Dvorak Apr 14 '17 at 14:14 • @JanDvorak sure doing it now. – Maltysen Apr 16 '17 at 0:17 # JavaScript (ES6), 52 46 bytes f=([[c,...s],...a])=>s+a?c+f(s+s?[...a,s]:a):c  Takes input as an array of strings and outputs as a single string. ### Test snippet f=([[c,...s],...a])=>s+a?c+f(s+s?[...a,s]:a):c g=a=>console.log("Input:",JSON.stringify(a),"Output:",JSON.stringify(f(a))) g(["SIMPLE"]) g(["POLLS","EPEES"]) g(["LYES","APRONS"]) g(["ABCDE","a c","123 567"]) g(["\"\\n$?*",",(.)\" "]) // Backslash and quote are escaped, but in/output are correct

• f=([[c,...s],...a])=>c?c+f([...a,s]):a+a&&f(a) – Neil Dec 8 '16 at 14:06
• @Neil That's a great approach. I managed to golf 6 bytes off my own :-) – ETHproductions Dec 8 '16 at 15:35

import Data.List
concat.transpose


Try it on Ideone. Usage:

Prelude Data.List> concat.transpose$["ABCDE","a c","123 567"] "Aa1B 2Cc3D E567"  ### Without using a build-in: (38 34 bytes) f[]=[] f x=[h|h:_<-x]++f[t|_:t<-x]  Try it on Ideone. 4 bytes off thanks to Zgarb! Usage: Prelude> f["ABCDE","a c","123 567"] "Aa1B 2Cc3D E567"  • You can remove all parens in the alternative version. Still won't beat the import though. – Zgarb Dec 8 '16 at 16:46 • Do you actually need the base case? – xnor Dec 8 '16 at 17:16 • Never mind, of course the base case is needed. – xnor Dec 8 '16 at 17:24 • @xnor You also can't move the base case to the end and replace it with f a=a to save a byte because both [] have a different type ... so close. – Laikoni Dec 8 '16 at 19:46 # C, 114 84 bytes -20 bytes for not calculating the length. i,b;f(char**s){b=1;while(b){i=-1;b=0;while(s[++i]>0)if(*s[i])putchar(*s[i]++),++b;}}  Accepts array of char pointers and requires last item to be a null-pointer (see usage). Ungolfed and usage: i,b;f(char**s){ b=1; while(b){ i=-1; b=0; while(s[++i]>0) if(*s[i]) putchar(*s[i]++),++b; } } int main(){ char*a[]={ // "POLLS","EPEES" // "LYES","APRONS" "ABCDE","a c","123 567" ,0}; f(a); puts(""); }  • Does the usage of printf/sprintf not allowed ? :D you would win quite some bytes. – Walfrat Dec 8 '16 at 14:18 • @Walfrat Without printing directly I'd need to allocate a string, so how could this save anything. – Karl Napf Dec 8 '16 at 14:22 • it was before your edit where you added the ++b and remove length compute, so yes can't work anymore. – Walfrat Dec 8 '16 at 14:26 • @Walfrat Yes, but i had a malloc and return before and this was longer than just printing – Karl Napf Dec 10 '16 at 18:50 # PHP, 68 67 bytes for(;$f=!$k=$f;$i++)for(;y|$v=$argv[++$k];$f&=""==$c)echo$c=$v[$i];  Loops over command line arguments. Run with -r. After the inner loop, $f is 1 when all strings are finished, 0 else (bitwise & casts ""==$c to int). Next iteration of the outer loop: copy $f to $k (saves one byte from $k=0) and toggle $f: When all strings are done, $f is now false and the loop gets broken.

• Doesn't work with empty input strings. Take a look at the last testcase – aross Dec 9 '16 at 11:01
• @aross: fixed. thanks. – Titus Dec 9 '16 at 14:26

## Retina, 13 bytes

Byte count assumes ISO 8859-1 encoding.

O$#.$.%
¶



Try it online!

### Explanation

O$#.$.%


This is based on the standard transposition technique in Retina. We sort (O) all non-linefeed characters (.), by ($#) the number of characters in front of them on the same line ($.%), i.e. their horizontal position.

The second stage then simply removes linefeeds from the input.

# Java, 19+155=174 160

String f(java.util.Queue<String> q){String s,r="";while(!q.isEmpty()){s=q.poll();r+=s.isEmpty()?"":s.charAt(0);if(s.length()>1)q.add(s.substring(1));}return r;}


Ungolfed:

  String f(java.util.Queue<String> q) {
String s, r = "";
while (!q.isEmpty()) {
s = q.poll();
r += s.isEmpty() ? "" : s.charAt(0);
if (s.length() > 1) {
}
}
return r;
}


Output:

SIMPLE

PEOPLELESS

LAYPERSONS

Aa1B 2Cc3D E567

",(n.$)?"* ​ First modification: merged string declaration to save some bytes. Removed import, it was used by the main() method (not shown here) that also needed LinkedList. It is fewer bytes to referece Queue directly. • initialize string s with string r can save few more – Syamesh K Dec 9 '16 at 11:10 • I know it's been almost a year ago, but you can golf a few bytes: String f(java.util.Queue<String>q){String s,r="";for(;!q.isEmpty();r+=s.isEmpty()?"":s.charAt(0))if((s=q.poll()).length()>1)q.add(s.substring(1));return r;} – Kevin Cruijssen Sep 6 '17 at 8:55 # PHP, 77 bytes ## Golfed function($a){for($d=1;$d!=$s;$i++){$d=$s;foreach($a as$v)$s.=$v[$i];}echo$s;}


Anonymous function that takes an array of strings.

I'm sure this could be golfed more, but it's early. On each iteration, we grab the i-th letter from each given string and append it to our final string, one at a time. PHP just throws warnings if we access bits of strings that don't exist, so that's fine. We only stop when no changes have been made after looping through all the strings once.

I feel like the usage of $d can be golfed more, but it's early. :P • How exactly do you put an array of strings in a single argument? – Titus Dec 8 '16 at 13:50 • @Titus. Y'know, I never really thought about it. I just kinda assumed you could. – Xanderhall Dec 8 '16 at 13:58 # Actually, 7 6 bytes Golfing suggestions welcome! Try it online! Edit: -1 byte thanks to Teal pelican. a Z♂ΣΣ  Ungolfing  Implicit input each string. a Invert the stack so that the strings are in the correct order. <space> Get the number of items on the stack, len(stack). Z Zip all len(stack) strings into one, transposing them. ♂Σ sum() every transposed list of chars into strings. Σ sum() again to join the strings together.  • Can you not remove the # to make it 6 bytes? – Teal pelican Dec 8 '16 at 15:44 • @Tealpelican Welp, now I'm going to have to dig through all of my old Actually answers and see if I can't change Z♂#Σ to Z♂Σ in all of them. Thanks for the tip :D – Sherlock9 Dec 8 '16 at 15:49 • First time looking into the language, it looks so much fun! Glad I could help :)) – Teal pelican Dec 8 '16 at 15:54 ## JavaScript (ES6), 46 bytes f=([[c,...s],...a])=>c?c+f([...a,s]):a+a&&f(a) <textarea oninput=o.textContent=f(this.value.split\n)></textarea><div id=o> # Python 2, 58 bytes lambda*m:''.join(map(lambda*r:''.join(filter(None,r)),*m))  Try it online! • Can't you remove the space in lambda *m? – Erik the Outgolfer Apr 16 '17 at 6:50 • I just did that! Thank you! – Keerthana Prabhakaran Apr 16 '17 at 6:56 # J, 13 bytes ({~/:)&;#\&.>  Try it online! Based on the inspiration for this question. Another way to do it takes 27 bytes but operates using transpose. Most of the bytes are to handle the automatically added zeroes from padding. [:u:0<:@-.~[:,@|:(1+3&u:)&>  ## Explanation ({~/:)&;#\&.> Input: list of boxed strings S &.> For each boxed string x in S #\ Get the length of each prefix from shortest to longest This forms the range [1, 2, ..., len(x)] Rebox it ( ) Operate on S and the prefix lengths &; Raze both /: Grade up the raze of the prefix lengths {~ Index into the raze of S using the grades Return  • J's prohibiting mixed arrays really hurts you here. Try it in APL. – Adám Dec 8 '16 at 15:11 # Bash + GNU utilities, 55  eval paste sed "s/.*/<(fold -1<<<'&')/g"|tr -d \\n\\t  I/O via STDIN (line-separated) and STDOUT. The sed formats each line to a bash process substitution. These are then evaled into paste to do the actual interleaving. tr then removes unnecessary newlines and tabs. Ideone. # PHP, 63 bytes Note: uses IBM-850 encoding for(;$s^=1;$i++)for(;n|$w=$argv[++$$i];s&=x<~■)echox=w[i];  Run like this: php -r 'for(;s^=1;i++)for(;n|w=argv[++$$i];$s&=$x<~■)echo$x=$w[$i];' "\"\n\$?*" "" ",(.)\" " 2>/dev/null;echo > ",\(n.$)?"*


# Explanation

for(                       # Iterate over string index.
;
$s ^= 1; # Continue until$s (stop iterating) is 1.
# Flip $s so each iteration starts with$s
# being 1.
$i++ # Increment string index. ) for( ; "n" |$w=$argv[++$$i]; # Iterate over all input strings. OR with "n" # to allow for empty strings. s &= x<~■ # If last character printed was greater than # \x0 (all printable chars), set s to 0, # causing the loop to continue. ) echo x = w[i]; # Print char i of current string.  • IBM-850?! Is that a natural encoding for PHP? – Adám Dec 9 '16 at 11:48 • @Adám what do you mean by "natural"? PHP treats bytes in the range 128-255 as text, which is therefore interpreted as a constant. If the constant is undefined, it will be interpreted as a string. It's so I can do ~■ (negated binary 254) instead of "\x1" (binary 1). – aross Dec 9 '16 at 13:02 • I see. It isn't that you actually need that codepage, you just need a 254 byte. – Adám Dec 9 '16 at 14:13 • @Adám yes, the codepage just makes it a printable char which is a little less annoying. – aross Dec 9 '16 at 14:27 • Great use of $$! – Titus Dec 9 '16 at 14:29 # Python 3, 75 Bytes I know the other Python one is shorter, but this is the first time I've used map ever in my life so I'm pretty proud of it lambda n:''.join(i[k]for k in range(max(map(len,n)))for i in n if len(i)>k)  # C, 75 71 bytes Only limitation is the output length. Currently it's 99, but can be easily stretched to 999 (+1 byte). i;main(a,b)char**b;{a--;for(;i<99;i++)*b[i%a+1]&&putchar(*b[i%a+1]++);}  Ungolfed: i; main( a, b ) char **b; { a--; for( ; i < 99; i++ ) *b[i % a + 1] && putchar( *b[i % a + 1]++ ); }  # Oracle SQL, 195 bytes  select listagg(b,'') within group(order by l,o) from(select substr(a,level,1) b,level l,o from i start with length(a)>0 connect by prior a=a and level<=length(a) and prior sys_guid() is not null)  Takes its input from a table named i with columns a (containing the string) and o (order of the string):  create table i (a varchar2(4000), a integer)  Explanation: We're exploiting CONNECT BY to break up the strings into each of the characters making them up. PRIOR SYS_GUID() being NOT NULL ensures we don't end up stuck in a loop. We then concatenate the single characters with LISTAGG but we shuffle them around with an ORDER BY clause, ordering them first by their position in the original string and only then by the string they came from. Not as short as the other answers but SQL isn't really meant as a string manipulation language :) ## Python 2, 128 96 I was hoping not to have to use itertools a=lambda a:"".join([i for i in reduce(lambda: b,c:b+c, map(None,*map(lambda m:list(m),a)) if i])  Ungolfed  a=lambda a: #Start a lambda taking in a "".join( #Join the result together with empty string [i for i in reduce( #For every item, apply the function and 'keep' lambda: b,c:b+c, #Add lists from... map(None,*map( #None = Identity function, over a map of... lambda m:list(m), a) #list made for mthe strings m ) if i #truthy values only (otherwise the outer map will padd with None. ])  • Would appreciate feedback/advice on improving this. – Pureferret Dec 9 '16 at 16:51 ## Perl 5, 28 bytes 26 bytes code + 2 for -0n. s/^./!print$&/gem while/./


Try it online!

# R, 73 bytes

for(i in 1:max(nchar(s<-scan(,""))))for(j in seq(s))cat(substr(s[j],i,i))


Try it online!

Explanation: very simple (but verbose), just loop through printing ith character of the jth string. Fortunately, substr returns an empty string if given an out-of-range input.

## Python, 112 bytes

i=len(x)if len(x)>len(y) else len(y) h=0 a="" while h<i: if h<len(x) a+=x[h] if h<len(y): a += y[h] h+=1 print a

• Your formatting is really messed up.. where do you even get x and y from? – Kade Dec 8 '16 at 13:35

"\",\\(n.$)? *"  The weave function is lazy, so it returns a list, which is why we have to force the result to a string. Being lazy, it can weave infinite sequences. For instance, we can weave the even and odd natural numbers, which are themselves infinite lazy lists: 5> (take 20 (weave (range 2 : 2) (range 1 : 2))) (2 1 4 3 6 5 8 7 10 9 12 11 14 13 16 15 18 17 20 19)  # K (oK), 35 29 bytes Solution: {c$r@&~^r:,/+(i$x)[;!#,/x]}  Try it online! Example: > {c$r@&~^r:,/+(i$x)[;!#,/x]}("ABCDE";"a c";"123 567") "Aa1B 2Cc3D E567" > {c$r@&~^r:,/+(i$x)[;!#,/x]}("\n$?*";"";",(.)\" ")
"\n,$(?.*)\" " > {c$r@&~^r:,/+(i$x)[;!#,/x]}("POLLS";"EPEES") "PEOPLELESS"  Explanation: Use 2nd-level indexing to pull out indices from 0 to max (length of flattened list) across all input lists. Any indexing beyond the bound of the sub-list will return a null. Flip (rotates 90), flatten, and then pull out the non-null results. Notes: • I cast to integer (i$) so that we get useful nulls, as space () is considered null for a char list which means you cant tell nulls from valid spaces.
• Also I couldnt get the TIO to work with input (worked fine in the oK repl) so the TIO link includes the "ABCDE"... example.

# Jq 1.5, 49 bytes

map(explode)|transpose|map(map(values)[])|implode


Explanation

                      # example input:          ["LYES","APRONS"]
map(explode)        # make list of ordinals   [[76,89,69,83],[65,80,82,79,78,83]]
| transpose           # zip lists               [[76,65],[89,80],[69,82],[83,79],[null,78],[null,83]]
| map(map(values)[])  # rm nulls and flatten    [76,65,89,80,69,82,83,79,78,83]
| implode             # convert back to string  "LAYPERSONS"


Sample Run

$paste input <(jq -Mrc 'map(explode)|transpose|map(map(values)[])|implode' input) ["SIMPLE"] SIMPLE ["POLLS","EPEES"] PEOPLELESS ["LYES","APRONS"] LAYPERSONS ["ABCDE", "a c", "123 567"] Aa1B 2Cc3D E567 ["\"\\n$?*", "", ",(.)\" "] ",\(n.$)?"*$ echo -n 'map(explode)|transpose|map(map(values)[])|implode' | wc -c
49
`

Try it online