Answer to life, the universe, and everything

Question

Task

Given a String as input, your task is to output 42 only if the input String happens to be exactly the following :

abbcccddddeeeeeffffffggggggghhhhhhhhiiiiiiiiijjjjjjjjjjkkkkkkkkkkkllllllllllllmmmmmmmmmmmmmnnnnnnnnnnnnnnoooooooooooooooppppppppppppppppqqqqqqqqqqqqqqqqqrrrrrrrrrrrrrrrrrrsssssssssssssssssssttttttttttttttttttttuuuuuuuuuuuuuuuuuuuuuvvvvvvvvvvvvvvvvvvvvvvwwwwwwwwwwwwwwwwwwwwwwwxxxxxxxxxxxxxxxxxxxxxxxxyyyyyyyyyyyyyyyyyyyyyyyyyzzzzzzzzzzzzzzzzzzzzzzzzzz

It may output any other value, produce an error or not output at all, if the input does not equal the aforementioned String.

---

Winning Criterion

This is code-golf, so the shortest code in bytes wins!

Answer 1

Golfscript, 20

26,{.97+\{.}*}%=42`*

with new line, 21 chars (by Nabb)

26,{).[96+]*}%n+=42`*

Actually Nabb beat mine, here is original solution for with new line, 22 chars

26,{.97+\{.}*}%n+=42`*

This is simply generating source string and just comparing it against string from stdin.

Answer 2

Ruby 1.9, 46 42 39 characters

p (?a..?z).map{|a|a*$.+=1}*""==gets&&42

Assumes the input isn't terminated with a newline.

Answer 3

C program - 78 89

Edit: Do not print 42 when there are extra characters.

Assumes input does not have a trailing newline.

main(i,j){for(i=1;i<27;i++)for(j=i;j--;getchar()==96+i?0:exit(1));puts("42"+!!gets(&i));}

If the prefix does not match, the program exits. If the prefix matches but there is 1-3 or so extra characters, prints 2. Otherwise, produces undefined behavior.

This can be made one character shorter by changing exit(1) to fork(). Oh, and on an unrelated note, remember to save any open documents in case, for whatever reason, your system happens to lock up.

Answer 4

PHP (60)

Assuming the input is provided in the commandline:

for(;$i<702;)$s.=chr(96.5+sqrt($i+=2));echo$s!=$argv[1]?:42;

Explanation: you can view the string as a triangle structure.

j     i   val
0     0   a
1   1-2   bb
2   3-5   ccc
3   6-9   dddd
4 10-14   eeeee
5 15-20   ffffff
      ...

Line j starts at index i = j*(j+1)/2 (that's the triangular number formula). Solving the quadratic equation results in index i being on line j = int((sqrt(8*i+1)-1)/2) and therefore containing character 97 + int((sqrt(8*i+1)-1)/2). The 0-350 index range allows us to simplify that to 96.5 + sqrt(2*(i+1)), but that no longer holds true for larger values.

Edit: Switched to commandline input as suggested in the comments.
Edit: Uses conditional operator to save a character

Answer 5

Perl, 35 43

map$s.=$_ x++$a,a..z;say 42if<>~~$s

Needs Perl 5.10 or later (run with -E), no newline in input.

I liked my side-effects regex better, but the shorter code has spoken. Here it is as a souvenir. Also intended for Perl 5.10 or later, but only for the advanced/experimental regex features, so only a p command-line option is needed.

$a=a;$_=/^(??{$b++;$a++."{$b}"}){26}$/&&42

Answer 6

05AB1E, 7 bytes (non-competing)

AƶJQi42

Try it online!

Explanation

A       push lowercase alphabet
 ƶ      lift every letter, push it and multiply it by its index
  J     join the list
   Qi   does it equal the input?
     42 push 42 and output implicitly

Just going through some challenges to learn 05AB1E (and golfing in general). This challenge was marked as active yesterday and I found a short solution, so why not share? :)

Answer 7

Haskell program - 71 67 64 57

Assumes no trailing newline, and does not output one either.

f x|x==[c|c<-['a'..'z'],_<-['a'..c]]="42"
main=interact f

Usage:

$ echo -n 'abbcccddddeeeeeffffffggggggghhhhhhhhiiiiiiiiijjjjjjjjjjkkkkkkkkkkkllllllllllllmmmmmmmmmmmmmnnnnnnnnnnnnnnoooooooooooooooppppppppppppppppqqqqqqqqqqqqqqqqqrrrrrrrrrrrrrrrrrrsssssssssssssssssssttttttttttttttttttttuuuuuuuuuuuuuuuuuuuuuvvvvvvvvvvvvvvvvvvvvvvwwwwwwwwwwwwwwwwwwwwwwwxxxxxxxxxxxxxxxxxxxxxxxxyyyyyyyyyyyyyyyyyyyyyyyyyzzzzzzzzzzzzzzzzzzzzzzzzzz' | { ./42; echo; }
42
$ echo -n 'something else' | { ./42; echo; }
42: 42.hs:1:0-54: Non-exhaustive patterns in function f


$

Answer 8

J, 29

f=:42#~((>:#a.{~97+])i.26)-:]

example:

f 'oasijfiojasef'

f 23841235

f 'abbccc...'
42

Answer 9

D: 94 Characters

void f(S)(S s){S t;foreach(i;0..26)t~=array(repeat(cast(char)(i+'a'),i+1));s==t&&writeln(42);}

More Legibly:

void f(S)(S s)
{
    S t;

    foreach(i; 0 .. 26)
        t ~= array(repeat(cast(char)(i + 'a'), i + 1));

    s == t && writeln(42);
}

Answer 10

Brachylog (2), 15 bytes, language postdates challenge

⊇Ạ∧?o?ọtᵐ~⟦₁+₁₆

Try it online!

And now for an answer which works on a completely different principle to most seen here. This is a function submission (the question doesn't specify what sort of submission is desired, but functions are permitted by default).

Explanation

This answer works by defining a sort of string: those which a) contain all lowercase letters of the alphabet, b) are in sorted order, and c) for which taking the number of occurrences of each character in the string produces a sequence of consecutive integers starting from 1. (It should be clear that there are many such strings, but the one we want to special-case is the shortest.) Then if the string fulfils those criteria, we add 16 to the number of distinct characters in the string; this will produce 42 if the string is the one the question asks us to special-case, and at least 43 in all other cases. (If the string fails any of the criteria to belong to the category, the function will end in failure, which is kind-of like throwing an exception.)

Here's how to interpret the source code:

⊇Ạ∧?o?ọtᵐ~⟦₁+₁₆
⊇Ạ               {the input} contains all lowercase letters
  ∧              and
   ?o?           the input sorts to itself
                 {and; implied when two conditions overlap}
     ?ọ          the {character, number of occurrences} pairs for the input
       tᵐ        when the second element of each is taken
         ~       create an output that could have been produced by
          ⟦₁     outputting the list of integers from 1 to some input inclusive;
            +₁₆  add 16 to that input {and output it}

Answer 11

R, 60 58

if(readline()==paste0(rep(letters,1:26),collapse=""))cat(42)

if(scan(,"")==paste(rep(letters,1:26),collapse=""))cat(42)

Thanks for the suggestion by @giusppe

Answer 12

Delphi, 164 132

This one builds a string and just compares it against the first command-line argument. It's shorter and less tricky than my other submission :

var s:string;c,i:int8;begin repeat s:=s+Char(c+97);i:=i-1;c:=c+Ord(i<0);if i<0then i:=c;until c=26;Write(42*Ord(s=ParamStr(1)));end.

(Note, that this version assumes that the c and i variables start out initialized at 0, as is the case in my version of Delphi (2010).)

Like my other submission, this one needs less characters if the string-building doesn't take place in a function, like I did before :

Delphi, 181

program a;{$APPTYPE CONSOLE}function s(c,i:byte):string;begin if(i>0)then Exit(Char(c)+s(c,i-1));if(c<122)then Exit(s(c+1,c-95));end;begin if(s(97,1)=ParamStr(1))then Write(42);end.

Note that the output doesn't need a newline, so WriteLn() became Write().

Answer 13

PHP - 45 characters

I'm surprise nobody posted any answer that used hashing. It's a very size effecient way of testing for exact string.

echo md5($argv[1],1)!='¯è a@ÛÚƒ:ïT�p'?:42;

The data is kind of hard to copy/paste since there is a null-byte in the middle of the code. Here's an hex-dump of the code for testing purposes.

65 63 68 6f 20 6d 64 35 28 24 61 72 67 76 5b 31 5d 2c 31 29 21 3d 27 af e8 a0 61 40 db da 7f 11 0f 83 3a ef 54 00 70 27 3f 3a 34 32 3b

Answer 14

Scala 79

 if((for(i <- 1 to 26;j<-1 to i)yield(96+i).toChar).mkString==args(0))print(42)

Answer 15

Pyth, 14

*42qzsm*dhxGdG

Just constructs the necessary string, then compares with the input and multiplies by 42.

Answer 16

K, 26 Bytes

{(::;42)x~,/(1+!26)#'.Q.a}
{(::;42)x~,/(1+!26)#'.Q.a}"hello"
{(::;42)x~,/(1+!26)#'.Q.a}"abbcccddddeeeeeffffffggggggghhhhhhhhiiiiiiiiijjjjjjjjjjkkkkkkkkkkkllllllllllllmmmmmmmmmmmmmnnnnnnnnnnnnnnoooooooooooooooppppppppppppppppqqqqqqqqqqqqqqqqqrrrrrrrrrrrrrrrrrrsssssssssssssssssssttttttttttttttttttttuuuuuuuuuuuuuuuuuuuuuvvvvvvvvvvvvvvvvvvvvvvwwwwwwwwwwwwwwwwwwwwwwwxxxxxxxxxxxxxxxxxxxxxxxxyyyyyyyyyyyyyyyyyyyyyyyyyzzzzzzzzzzzzzzzzzzzzzzzzzz"
42

Thanks

Answer 17

APL (Dyalog), 18 17 bytes

42/⍨⍞≡819⌶⎕A/⍨⍳26

Try it online!

Four obvious bytes can be saved if we are allowed to use uppercase.

42 42

/⍨ if (lit. replicated by)

⍞ character input

≡ is identical to

819⌶ the lowercased

⎕A Alphabet

/⍨ replicated by

⍳ one through

26 26

Answer 18

Python (84)

Assumes a trailing newline at the end of the input.

import sys
if''.join(c*chr(c+96)for c in range(27))+'\n'==sys.stdin.read():print 42

Answer 19

JavaScript (91 93 94 98 102 116)

Usage: a('string'), returns 42 if valid according to spec, or 0.

function a(z){for(i=r='';i++<26;)for(j=i;j--;)r+=String.fromCharCode(i+96);return(z==r)*42}

http://jsfiddle.net/g25M3/6/

Edit: Removed var and eliminated two spaces in for (.

Edit 2: Changed j>0 to j, and

1. return (z==r)?42:0; to
2. return z==r?42:0

Edit 3: Initialize i with i='', change

1. (z==r)?42:0 to
2. (z==r)*42

Edit 4: Change

1. for(;i<27;i++) to
2. while(i++<26)

Edit 5: Change

1. i=r='';while(i++<26) to
2. for(i=r='';i++<26;) and
3. for(j=i;j;j--) to
4. for(j=i;j--;)

Answer 20

PHP 92 88 87 chars

function _($a){for($i=97;$i<123;$i++)for($j=$i-96;$j;$j--)$b.=chr($i);echo($b==$a)*42;}

EDIT

Replaced $j<0 with $j and return $b==$a?42:0; with echo $b==$a?42:0;

Replaced echo $b==$a?42:0; with echo($b==$a)*42;

Answer 21

Python - 62 chars

print("".join(x*chr(x+96) for x in range(27))==raw_input())*42

Answer 22

Perl, ₄₉ 46 characters

to be used in a program, not on the command line

$..=chr($+96)x$ for 1..26;$.eq(pop)&&print '42'

join('',map$_ x++$x,'a'..'z')eq pop&&print'42'

Regards

rbo

_{Edit: Idea ripped from Ventero}

Answer 23

ECLiPSe Prolog - 173

c(_,[],_):-!. c(A,M,N):-length(L,N),checklist('='(A),L),append(F,L,M),P is N-1,B is A-1,c(B,F,P). ?- read_string(end_of_file,351,S),string_list(S,L),c(122,L,26),writeln(42).

Answer 24

05AB1E, 7 bytes

AƶJQ42*

Try it online!

---

Wellp, 05AB1E keeps evolving.

Answer 25

JavaScript 1.8, 99 chars

function c(x)(x.replace(/([a-z])\1*/g,function(m)!(a-m.length)*m.charCodeAt(0)-96-a++,a=1)==0)*a+15

I dare you to make sense of it :)

Answer 26

PHP - 59

Assumes at least 1 input is provided over cli

echo md5($argv[1])!='afe8a06140dbda7f110f833aef540070'?:42;

It more or less works, except that md5 is can technically have duplications with the hashing algo.

Answer 27

VBA 91

There weren't any VBA answers but this works:

Function f(t)
    For i = 1 To 26
        o = o & String(i, Chr(i + 96))
    Next
    f = -42 * (t = o)
End Function

Answer 28

PowerShell v2+, 47 bytes

42*(-join(1..26|%{,[char]($_+96)*$_})-ceq$args)

Constructs a range 1..26, feeds that through a loop with |%{...}. Each iteration we use the comma operator to construct an array literal of the current [char] multiplied by the current loop number. We then -join that all together to construct the string abbcccdddd... and then use a case-sensitive -ceq comparison against our input $args, which will result in either $TRUE or $FALSE. In PowerShell, Boolean values can be implicitly cast as 1 or 0, respectively, which is what happens here with the 42*. Will print out 42 iff the input is abbccc...zzzzzzzzzzzzzzzzzzzzzzzzzz and will output 0 otherwise.

Answer 29

05AB1E, 14 13 bytes, non-competing

AvyN>×}JIQi42

Try it online!

Edit: Saved 1 byte thanks to @Okx.

My first official PPCG submission!

Explanation:

AvyN>×}JIQi42

A              # push alphabet to stack
 v    }        # foreach in ToS, element = y, index = N
  y            # push letter to stack
    N>         # increment index by 1
     ×         # repeat the letter (index + 1) times, push to stack

       J       # join stack together
        I      # push input to stack
         Q     # check if string == input
          i42  # if so, push 42 to stack, implicitly print

Answer 30

Jelly, 13 bytes in Jelly's codepage, language postdates challenge

26RØa,ZŒṙ⁼×42

Try it online!

Explanation

26RØa,ZŒṙ⁼×42
     ,         Start with a pair of:
   Øa            the lowercase alphabet (['a', 'b', …, 'y', 'z'])
26R              and the list [1, 2, 3, 4, …, 25, 26]
      Z        Swap rows and columns (yielding [['a', 1], ['b', 2], …, ['z', 26]])
       Œṙ      Run-length decode (yielding the string in the original question)
         ⁼     1 if equal to {the original input}, 0 otherwise
          ×42  Multiply by 42

So we end up outputting 42 if the string is the special-cased string, or 0 otherwise.

Answer 31

Pyth, 10 bytes (non-competing)

*42qSs.__G

Explanation:

*42qSs.__G
        _G     Reversed alphabet "zyx...a"
      ._       Prefixes ["z", "zy", ..., "zyx...a"]
    Ss         Concatenated and sorted "abbccc...zzz"
   q      Q    Compare with implicit input
*42            42 if the input matches, 0 otherwise

Answer 32

Excel VBA, 50 Bytes

Anonymous VBE immediate window function that takes input from cell [A1] and outputs 42 iff the input is equal to the expected output, else 0

For i=1To 26:s=s+String(i,i+96):Next:?([A1]=s)*-42

Answer 33

Python, 56 bytes

lambda s:s=="".join(c*chr(c+96)for c in range(27))and 42

I know I'm late to the party, but both of the existing Python answers were full programs, which seemed suboptimal. Returns 42 for the specified input, False for everything else.

Answer 34

05AB1E, 9 bytes (non-competing)

ASā×JQi42

Try it online!

Explanation

ASā×JQi42   Argument: s
AS          Push alphabet as array
  ā×J       Each character as many times as its index
     Q      Compare with s
      i42   If true, output 42

Answer 35

Perl 6, 32 bytes

{42 if $_ eq[~] 'a'..'z'Zx 1..*}

Answer 36

Javascript, 145 bytes

Only uses recursion

((function(i,k,l){return(String.fromCharCode(97+i)==l[k+i])&&((i<25)?arguments.callee(++i,k+i,l):l.length==k+i+1)}).call(this,0,0,line)==true)*42

This approach checks each character along the way instead of creating the valid string to compare against. So, is the 'g' actually in the correct position, then return true. Finally check that the length is what is expected. Any falses on the way cause a '0' to be returned.

Thanks for the hint regarding the *42 at the end

Answer 37

Lua 98

i=io.read()e=0 for k=1,26 do s,e=i:find(string.char(96+k):rep(k),e+1)_=e or os.exit()end print(42)

Answer 38

Clojure - 61 chars

(fn[a](if(=(mapcat #(repeat%(char(+% 96)))(range 1 27))a)42))

Exploits the following facts:

• Clojure can interpret any string automatically as a sequence of chars
• I can use the range of numbers from 1 to 26 to both create the characters and repeat them the correct number or times to generate the "correct" input

Answer 39

Delphi, 127

var b:Char;c,i:Int8;begin repeat if i<0then i:=c;Read(b);if c+97<>Ord(b)then Exit;i:=i-1;c:=c+Ord(i<0)until i=27;Write(42);end.

This one reads the string from the input, compares it as it goes, writes 42 when the input matches up until the last z.

Delphi, 157

var b:pchar;c,i:byte;begin b:=CmdLine+85;c:=97;i:=1;repeat Inc(b);if b^<>Char(c)then Exit;Dec(i);if i>0then Continue;c:=c+1;i:=c-96;until i=27;Write(42);end.

Delphi, 188

program a;{$APPTYPE CONSOLE}var b:pchar;c,i:byte;begin b:=CmdLine+85;c:=97;i:=1;repeat Inc(b);if(b^<>Char(c))then Exit;Dec(i);if(i>0)then Continue;c:=c+1;i:=c-96;until(i=27);Write(42);end.

This version doesn't use a function, which saves quite a few characters when compared to the previous version of this technique :

Delphi, 213

program a;{$APPTYPE CONSOLE}function t(b:pchar;c,i:byte):byte;begin repeat Inc(b);if(b^<>Char(c))then Exit(0);Dec(i);if(i>0)then Continue;c:=c+1;i:=c-96;until(i=27);t:=42;end;begin WriteLn(t(CmdLine+77,97,1));end.

Alas a bit long, mostly because Delphi's long keywords, and the need to initialize console applications before they can write output.

Also note that I incremented CmdLine by 77 characters, as that was the offset I needed to skip over my local executablepath (Delphi has no direct argument pointer). Adjust to match your own setup (could lead to 1 less character when offset < 10).

Answer 40

C (gcc), 86 bytes

i,c;main(a){for(i=0;i++<a&&(c=getchar())==a+96;);a>26&&c<0?puts("42"):i>a&&main(a+1);}

Try it online!

Answer 41

C++ (110 chars)

Assumes use of the std namespace, headers, etc. And make use of everything not specified in the question (whether it can output something else when the string doesn't match, etc.)

int main(int, char **c)
{
    string s(c[1]), t;
    for(int i=1; i < 27; i++) {
        for(int j=0; j < i; j++) {
            t += i+96;
        }
    }
    cout << 42 + s.compare(t);
}

Answer 42

Husk, 12 10 bytes

&42=ṘN…"az

-2 bytes thanks @Zgarb!

Try it online!

       "az  -- constant string: "az"
      …     -- fill the range 'a'..'z': "abc...xyz"
    ṘN      -- replicate each character [1..] times: "abbccc...zzz..z"
   =        -- is input equal to that string?
&42         -- if it is then 42 else 0

Answer 43

Javascript 144

Probably can be significantly improved, recursion has always been a head far for me.

Compressed

function r(a,b,d,c){c++;if(b<d)a+=r(a,b+1,d,c);for(i=0;i<c;i++)a=String.fromCharCode(b)+a;return a}function q(a){if(q==r(a,97,122,0))return 42};

Less Compressed

function r(s, c, x, w){        
    w++;
    if(c < x)
        s += r(s, c + 1, x, w);
    for(i = 0; i < w; i++)
        s = String.fromCharCode(c) + s;              
    return s;
}
function q(z){
    if(q==r(z,97, 122, 0))
        return 42;            
}

alert(q("rgrg"));

Answer 44

Japt, 11 bytes

;¶CËpEÄ
*42

Try it

Answer 45

Zsh, 97 56 52 51 bytes

Builds the string then compares $1. If the input doesn't match the magic string, some integer other than 42 (or an error message) is printed. Try it online!!

for c ({a..z})repeat $[++i];s+=$c
<<<$[${#s#$1}+42]

_{My original solution: 97bytes (ascii evaluate input)
@GammaFunction's solutions: 56bytes 52 bytes 51 bytes (main solution)
Example: for c ({a..z})s+=${${(l:++i:)}//?/$c};[ $s = $1 ]&&<<<42}

Answer 46

Bash, 68 bytes

for c in {a..z};{ for ((i=++j;i--;)){ s+=$c;};}
[ $s = $1 ]&&echo 42

Build the string, compare and print. If the input string has spaces in it, the [ comparison ] will break, but return falsy anyway.

Try it online!

Answer 47

Groovy - 64

print args[0]!=(1..26).collect{"${(char)it+96}"*it}.join()?'':42

Answer 48

Burlesque, 24

@azr@{J**96.-.*}ms==42.*

Pretty standard solution.

@az r@            creates range from 'a to 'z
{                 start mapping the code block to each element
    J ** 96 .-    duplicates the current and gets it position in the alphabet (n)
    .*            duplicates the element n times
}ms               end mapping, with the added flourish to concatenate the mapped block
==42.*            got this from isaacg above me.

Try it here. Note that Burlesque takes anything that's before the code as input, so mess up the "abb...zzz" string to see it fail.

Answer 49

C++, 157 154

Compressed (headers included) [154 characters]:

#include<iostream> 
#include<string>
int i,j;int main(){std::string h;std::cin>>h;for(;i<26;i++)while(j<=i+i*(i+1)/2)(h[j]=='a'+i)?j++:j;std::cout<<42;}

Compressed (headers and using namespace std assumed like in this answer) [100 characters]:

int i,j;int main(){string h;cin>>h;for(;i<26;i++)while(j<=i+i*(i+1)/2)(h[j]=='a'+i)?j++:j;cout<<42;}

Not compressed (with headers):

#include <iostream>
#include <string>
using namespace std;

int i, j;
int main()
{
    string h;
    cin >> h;
    for(i = 0 ; i < 26 ; i++)
        while(j <= i+i*(i+1)/2)
            (h[j] == 'a'+i)?j++:j;
    cout << 42;
}

Explanation:

• int i,j; int main(): i and j are initialized to 0 with 8 characters instead of 12 (int i=0,j=0;)
• j<=i+i*(i+1)/2: use of the triangular number formula
• (h[j]=='a'+i)?j++:j: endless loop trick when j is not incremented

Edit. Headers and using statements counted

Answer 50

Q, 31 30

{$[x~(,/)(1+(!)26)#'.Q.a;42;]}

Answer 51

J, 21 bytes

Program:

   42*(u:96+(]#])i.27)-:

Usage:

   42*(u:96+(]#])i.27)-: 'abbcccddddeeeeeffffffggggggghhhhhhhhiiiiiiiiijjjjjjjjjjkkkkkkkkkkkllllllllllllmmmmmmmmmmmmmnnnnnnnnnnnnnnoooooooooooooooppppppppppppppppqqqqqqqqqqqqqqqqqrrrrrrrrrrrrrrrrrrsssssssssssssssssssttttttttttttttttttttuuuuuuuuuuuuuuuuuuuuuvvvvvvvvvvvvvvvvvvvvvvwwwwwwwwwwwwwwwwwwwwwwwxxxxxxxxxxxxxxxxxxxxxxxxyyyyyyyyyyyyyyyyyyyyyyyyyzzzzzzzzzzzzzzzzzzzzzzzzzz'
42

Explanation:

   42*                    NB. Multiply 42 to
      (
       u:                 NB. Convert all to characters
         96+              NB. Add 96 to all
            (]#])         NB. "]" copies the i.27, and 1 4 # 1 2 gives 1 2 2 2 2 for example
                 i.27     NB. 0 1 2 3 ... 26 (not 27)
                     )
                      -:  NB. matches the right hand side (return 1 if matches, 0 otherwise)

Answer 52

Reng v.3.2, 88 bytes

(Noncompeting, postdates question.)

2#y2#z"a"1Ø         Ø3r1\
:1+>y1-?!v$z1+:#y#zRzeq!^
   ^  :y#<
i sve(*?v)
?~n>$ 2.>076**

This is one heckuvan answer.

Initial

2#y2#z"a"1Ø

Stores 2 to y (the temporary counter) and z (the overall counter), and initiates the stack with "a" then goes to the next line.

Loop

:1+>y1-?!v$z1+:#y#zRzeq!^
   ^  :y#<

First, :1+ duplicates the previously made run of characters and increments it to work with the next one. Then...

Generating N copies of a number

   >y1-?!v
   ^  :y#<

This loops until y == 0. Once y is zero, we exit the loop. Otherwise, we put y - 1 back into y and duplicate the character being worked with it.

Breaking out of this loop

          $z1+:#y#zRzeq!^

This drops y from the conditional and increments and duplicates z, which is then put into y and z. Then, if R (26 + 1) is z, we go to the next part. Otherwise, the loop continues again.

Transition

                    Ø3r1\
                        ^

This goes out of the loop, pushes 1 (our equality counter), reverses the stack, and goes to the third line.

Final

i sve(*?v)
?~n>$ 2.>076**

i sve(*?v) loops until (a) there is no input or (b) the equality counter is 0. In the first case, the first v is met, and we drop the -1 bit, skip over the >0 bit (2.), and output 42 (6*7*equality), skipping ~ with a conditional. Otherwise, the second v is encountered, and a zero is pushed before the 76**, so this makes it zero. The conditional activates the ~ (exit program) command because the TOS is falsey, and thus no output is given.

Answer 53

SmileBASIC, 58 bytes

DEF F S
FOR I=1TO 26C$=C$+CHR$(I+64)*I
NEXT?42OR C$!=S
END

I had to make it a function since the maximum INPUT length is 128 characters.

Answer 54

R, 74 bytes

g=function(x){if(x==paste(rep(rep(letters[1:26]),(1:26)),collapse=""))42}

Answer 55

Java 8, 103 101 87 bytes

s->{String r="";for(char c=96,i;++c<123;)for(i=96;i++<c;)r+=c;return r.equals(s)?42:0;}

Returns 0 for everything that doesn't match the expected input.

Explanation:

Try it here.

s->{                       // Method with String parameter and integer return-type
  String r="";             //  String starting empty
  for(char c=96,i;++c<123;)//  Loop (1) over the lowercase alphabet:
    for(i=96;i++<c;)       //   Inner loop (2) `c-i` amount of times:
      r+=c;                //    Append that many of the current letter to the String
                           //   End of inner loop (2) (implicit / single-line body)
                           //  End of loop (1) (implicit / single-line body)
  return r.equals(s)?      //  If the input equals the String:
    42                     //   Return 42
   :                       //  Else:
    0;                     //   Return 0
}                          // End of method

Answer 56

Axiom, 141 bytes

f(x:String):NNI==(c:=96;i:=0;k:=1;repeat(c:=c+1;i:=i+1;for j in 1..i repeat(k>#x or ord(x.k)~=c=>return 0;k:=k+1);c=122=>break);k=#x+1=>42;0)

ungolf

--It would return 42 if the string in input it is as string above this codegolf question 
--it would return 0 in other cases; suppose Axiom ord() return 97..122 for a..z (ascii)
ff(x:String):NNI==
   c:=96;i:=0;k:=1
   repeat
      c:=c+1; i:=i+1           -- c='a'=97 i=1 k=1
      for j in 1..i repeat
               k>#x or ord(x.k)~=c=>return 0
               k:=k+1
      c=122=>break -- c==122 is 'z'
   k=#x+1=>42
   0

Answer 57

Japt, 13 12 11 bytes

Outputs 42 or false.

;¶CËpEÄé#*

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Answer 58

Python 3, 58 bytes

lambda s:[42][''.join([i*chr(i+96)for i in range(27)])!=s]

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Six years late to the party?

golfed 4 bytes off when I realized I could've used != instead of 1- ==

Answer 59

JavaScript, 86 Bytes

c="";for(x=0;x<26;)c+=String.fromCharCode(x+97).repeat(++x);alert(prompt("")==c?42:0);

White spaced:

c="";
for(x=0;x<26;)
    c+=String.fromCharCode(x+97).repeat(++x);
alert(prompt("")==c?42:0);

I couldn't indent by 4 spaces for some reason. Not sure if using alert is allowed.

Edit: Fixed indent

Answer 60

Jelly, 9 bytes

ØaxJ¤⁼×42

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There is already a 13 byte Jelly answer, but the user had their account deleted, and it felt wrong to just edit in this code.

How it works

ØaxJ¤⁼×42 - Main link. Argument: s (string)   e.g. "abc"
Øa  ¤     - Yield the lowercase alphabet           "abc...xyz"   
   J      - Yield range(length)                    [1 2 ... 25 26]
  x       - Repeat (vectorising).                  "abbccc..."
     ⁼    - Equal to the input? Call the A         0
      ×42 - Multiply 42 by A                       0

Answer 61

Pyth - 21 Bytes

V26=Y+Y*@GNhN;IqsYz42  

Explanation:

V26=Y+Y*@GNhN;IqsYz42  z is initialised to input and Y to empty list
V26                    For N from 0 to 25
   =Y                  Set Y to
      Y                Y
     +                 Plus
        @GN            Item N of the alphabet
      *                Times
           hN          N plus one
             ;         End For
              I        If
                sY     Concatenate all elements of Y       
               q       Equals
                  z    z  
                   42  Print 42   

Answer 62

Javascript (ES6) 84 bytes

s=>[...Array(26)].map((_,i)=>String.fromCharCode(97+i).repeat(i+1)).join("")==s?42:0

I don't think an explanation is needed, but here's one anyway:

s=> // input
    [...Array(26)] // preparing alphabet array
    .map((_,i)=>String.fromCharCode(97+i).repeat(i+1)) // using the current index to get the corresponding letter and repeat it as many times as it's 1-index
    .join("")==s?42:0 // Join the array into a string and check if equal to input.

Answer 63

APL NARS 14 chars

{⍵≡⎕a/⍨⍳26:42}

it return 42 for the request string, nothing if something else.

  f←{⍵≡⎕a/⍨⍳26:42}
  w←(⍳26)/⎕a
  f 2
  f w
42
  f 'str'

Answer 64

Sinclair ZX81/Timex TS1000/1500 BASIC, ~138 tokenized BASIC bytes

 1 LET A$="A"
 2 LET C=NOT PI
 3 FOR I=SGN PI TO VAL "25"
 4 LET A$=A$+CHR$ (CODE "A"+I)
 5 LET C=C+SGN PI
 6 IF C<=I THEN GOTO VAL "4"
 7 LET C=NOT PI
 8 NEXT I
 9 INPUT B$
10 IF A$=B$ THEN PRINT "42"

This is the most byte efficient solution I could think of for the technology in question (whilst retaining readability, of course), however, building the string A$ does take a while so be patient (or set an emulator to a decent speed above 3.5Mhz).

Answer 65

AWK, 65 bytes

{for(;i<26;)for(j=++i;j--;)L=L sprintf("%c",i+96);$0=L==$0?42:0}1

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Maybe I should develop a golfing version of AWK, but until then, here is my AWK solution :)

Answer 66

K (oK), 14 bytes

Solution:

42*(&!27)~-96+

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Explanation:

Returns 42 if the input matches the "abbccc..." otherwise 0.

42*(&!27)~-96+ / the solution
          -96+ / subtract 96 from the input (vectored)
         ~     / matches?
   (&!27)      / where (&) til (!) 27. Generates 1 2 2 3 3 3 4 4 4 4... sequence
42*            / multiply result (0 false or 1 true) by 42

Answer 67

Python 2, 69 bytes

x=""
for i in range(26):x+=chr(97+i)*(i+1)
if raw_input()==x:print 42

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Answer 68

Julia 0.6, 55 bytes

s->join("$c"^i for (i,c) in enumerate('a':'z'))==s?42:0

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Answer 69

Lua, 80 bytes

c=""for i=1,26 do c=c..string.char(i+96):rep(i)end print(c~=io.read()and""or 42)

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Brief explanation: creates the string and then compares it with the input. Output is an empty string or 42.

Answer 70

Wren, 72 bytes

Generate the range 'a'..'z'. Multiply the string-converted value by the value - 96. Join the list. Check whether the input is equal to this string.

Fn.new{|A|A==(1..26).map{|x|String.fromCodePoint(x+96)*(x)}.join()?42:0}

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Answer 71

Groovy, 70

a=[];(1..26).each{a+=[(char)it+96]*it};if(args[0]==a.join(''))print 42

Answer 72

C++

$ cat main.cpp | wc -m -l
16     269

Not compressed

Recursive ok routine checks string for abbcccdddd....

#include <iostream>

bool ok(char *c)
{
    char *s = c;
    while(*c && *c == *s) c++;
    return (c - s == *s - 'a' + 1) && ((*c == 0 && *s == 'z') || ok(c)); 
}

int main(int c, char **v)
{
    if(c > 1 && ok(v[1]))
        std::cout << 42 << std::endl;

    return 0;
}

Second version

$ cat main.cpp | wc -m -l
15     239

Without recursion

#include <stdio.h>

bool ok(char *c)
{
    char i,j;
    for(i = 'a'; i <= 'z'; ++i)
    for(j = 'a'; j <= i; ++j)
        if(*c++ != i) return 0;
    return !*c;
}

int main(int c, char **v)
{
    return c > 1 && ok(v[1]) && printf("42"), 0;
}

Answer 73

Javascript, 104

function f(x){var a="";for(b=97;b<123;b++)a+=Array(b-95).join(String.fromCharCode(b));if(x==a)return 42}

Should be pretty obvious, but it creates the string and then tests it against the input.

If I can golf this down any further, please let me know.

Answer 74

JavaScript (1.8), 103 characters

function f(s,i)i===+i?s.length-i-1||s.charCodeAt()-i-97:s&&s.match(/(.)\1*/g).some(f)+s.length!=351|42

Here's my rather long attempt in JavaScript... returns 42 if the string is the valid string, 43 otherwise.

Here's a prettier, earlier version with whitespace:

function f(s) {
  return s && s.match(/(.)\1*/g).some(function(x,i) {                
    return x.length-i-1 || x.charCodeAt()-i-97
  })+s.length==351 && 42
}

and another version, closer to the final version (modulo whitespace removal)

function f(s,i) {
  return i===+i
       ? s.length-i-1 || s.charCodeAt()-i-97
       : s&&s.match(/(.)\1*/g).some(f)+s.length!=351 | 42
 }

Answer 75

R, 99

f=function(x){s="";for(i in 1:26)s=c(s,(rep(letters[i],each=i)));s=paste(s,collapse="");if(x==s)42}

Usage:

f("test")
f("abbcccddddeeeeeffffffggggggghhhhhhhhiiiiiiiiijjjjjjjjjjkkkkkkkkkkkllllllllllllmmmmmmmmmmmmmnnnnnnnnnnnnnnoooooooooooooooppppppppppppppppqqqqqqqqqqqqqqqqqrrrrrrrrrrrrrrrrrrsssssssssssssssssssttttttttttttttttttttuuuuuuuuuuuuuuuuuuuuuvvvvvvvvvvvvvvvvvvvvvvwwwwwwwwwwwwwwwwwwwwwwwxxxxxxxxxxxxxxxxxxxxxxxxyyyyyyyyyyyyyyyyyyyyyyyyyzzzzzzzzzzzzzzzzzzzzzzzzzz")
[1] 42

Answer 76

Oracle SQL 11.2, 148 bytes

SELECT 42 FROM(SELECT MAX(TRANSLATE(SYS_CONNECT_BY_PATH(LPAD(' ',LEVEL+1,CHR(64+LEVEL)),';'),'A; ','A'))s FROM DUAL CONNECT BY LEVEL<27)v WHERE:1=s;

Answer 77

Haskell, 45 51 bytes

f x|x==zip[1..]['a'..'z']>>=uncurry replicate->"42"

zip [1..] ['a'..'z'] produces the list [(1,'a'), (2,'b'), ...].

uncurry replicate has the type (Int, a) -> [a], and uncurry replicate (n, v) produces a list of n copies of v.

>>= applies uncurry replicate to the zipped list, and concatenates the results.

Finally, that string compared to the argument and returns "42" if it is equal, or crashes.

(edited b/c I'm dumb and didn't notice the return requirement)

Answer 78

Pylongolf2, 21 bytes

con1968701440=?42~¿

Explanations:

con1968701440=?42~¿
c                   read input
 on                 hash it and then convert into integer
   1968701440       push the (aaa.zz) thing (but hashed) into the stack
             =      compare them
              ?     if true,
               42~  output 42
                  ¿ end if statement.

That last inverted question mark messed me up by 2 bytes :|