I know you, but you don't know me

Question

You're tasked with writing two programs. Program A must print out nothing on all inputs except when program B is input, in which case it should print 1. Program B must print out 1 on all inputs except when program A is input, in which case it should print nothing.

Scoring:

• +1 For each character from both programs.
• Lowest score wins.

Answer 1

GTB, 25

Executed from a TI-84 calculator

Program A

`_@_eq;"$w;&

Program B

`_@_eq;"$#w;&

Explanation

`_ Input a string

@_eq;" Check if it equals the source code (# is automatically stripped along with lowercase letters)

$w;& If so, display 1 (otherwise nothing) [for B it's $#w;& - if not, display 1 (otherwise nothing)]

Answer 2

Bash - 32 characters

Script A - 16 characters

cmp -s b&&echo 1

Script B - 16 characters

cmp -s a||echo 1

Usage

$> echo "foo" | ./a
$> cat b | ./a
1
$> echo "foo" ./b
foo ./b
$> cat a | ./b

Answer 3

Ruby, 54

A

$><<1if$<.read==IO.read(?B)

B

$><<1if$<.read!=IO.read(?A)

examples:

bash-3.2$ ruby A < A
bash-3.2$ ruby A < B
1bash-3.2$ ruby B < A
bash-3.2$ ruby B < B
1bash-3.2$ 

Answer 4

J (62)

Since you didn't forbid this...

Store the programs as A and B respectively.

Program A (30):

exit echo#~(1!:1<'B')-:1!:1[3

Program B (32):

exit echo#~-.(1!:1<'A')-:1!:1[3

How it works (Program B, A is similar):

• 1!:1[3: read stdin
• 1!:1<'A': read file A
• -:: see if they are equal
• -.: negate the result
• #~: replicate the result by itself (so, 1 results in one 1 and 0 results in zero 0s, i.e. nothing)
• echo: output
• exit: exit (the J interpreter does not exit by default when it reaches the end of the file)

$ jconsole A <B
1
$ jconsole A <foo
$ jconsole B <A
$ jconsole B <foo
1
$

Answer 5

Haskell - WITHOUT loading source - 478 644 characters

This assumes getContents ALWAYS ends with a newline and so drops the final character without checking because I don't feel like escaping it

A

main=interact$($'1').replicate.(1-).fromEnum.(/=map r(d++shows d[toEnum 10]))where r n|n=='-'='*'|n=='*'='-'|True=n;d="main=interact$($'1').replicate.(1-).fromEnum.(/=map r(d++shows d[toEnum 10]))where r n|n=='-'='*'|n=='*'='-'|True=n;d="

B

main=interact$($'1').replicate.(1*).fromEnum.(/=map r(d++shows d[toEnum 10]))where r n|n=='*'='-'|n=='-'='*'|True=n;d="main=interact$($'1').replicate.(1*).fromEnum.(/=map r(d++shows d[toEnum 10]))where r n|n=='*'='-'|n=='-'='*'|True=n;d="

It works like a standard quine, but swapping - for * to get the other program (avoiding those characters elsewhere).

The following test prints as expected (replacing main=interact$ with a= and b=)

main=do
  putStrLn "START"
  putStrLn$a "FOO"
  putStrLn$a "main=interact$($'1').replicate.(1*).fromEnum.(/=map r(d++shows d[toEnum 10]))where r n|n=='*'='-'|n=='-'='*'|True=n;d=\"main=interact$($'1').replicate.(1*).fromEnum.(/=map r(d++shows d[toEnum 10]))where r n|n=='*'='-'|n=='-'='*'|True=n;d=\"\n"
  putStrLn$b "FOO"
  putStrLn$b "main=interact$($'1').replicate.(1-).fromEnum.(/=map r(d++shows d[toEnum 10]))where r n|n=='-'='*'|n=='*'='-'|True=n;d=\"main=interact$($'1').replicate.(1-).fromEnum.(/=map r(d++shows d[toEnum 10]))where r n|n=='-'='*'|n=='*'='-'|True=n;d=\"\n"
  putStrLn "END"

-

START

1
1

END

Answer 6

Python 2.7 - 82

File A (literally named just a):

if raw_input()==open('b').read():print 1

File B (literally named just b):

if raw_input()!=open('a').read():print 1

Answer 7

Ruby, 166 chars, no reading source

A:

(gets(p)==<<2.tr('&|','|&')*2+'2')&&p(1)
(gets(p)==<<2.tr('&|','|&')*2+'2')&&p(1)
2

B:

(gets(p)==<<2.tr('|&','&|')*2+'2')||p(1)
(gets(p)==<<2.tr('|&','&|')*2+'2')||p(1)
2

Make sure your text editor doesn't save with a trailing newline.

Usage (example):

 $ ruby know_a.rb know_b.rb 
1
 $ ruby know_a.rb know_a.rb 
 $ ruby know_b.rb know_a.rb 
 $ ruby know_b.rb know_b.rb 
1

Each program constructs the source of the other program using a HEREdoc and string transforms, then compares the result to the input.

Answer 8

Python 3 - 102 characters

Prints 1 if the input is the same as program 2, otherwise nothing:

if input()==open('a.py').read():print('1')

Prints 1 if input is not the same as program 1, otherwise nothing:

if input()==open('a.py').read():print('1')

Answer 9

Haskell - 138

Not really a good answer, but wanted to make both programs use the same source. Could save some chars by renaming the file, but it's not going to make this a winning solution so I don't think it's worth it.

import System.Environment
import Control.Monad
main=do{i<-getContents;p<-getProgName;f<-readFile "ab.hs";when((f==i)/=(p=="B"))(print 1)}

Compile this source as both A and B.

Test:

% ghc -o A ab.hs
[1 of 1] Compiling Main             ( ab.hs, ab.o )
Linking A ...
% cp A B
% ./A < ab.hs
1
% ./B < ab.hs
% ./A < ab.hi
% ./B < ab.hi
1

Answer 10

Node.js - 142 characters

Script | (otherwise known as Script A) - 80 characters

f=require('fs').readFileSync;f('/dev/stdin','hex')==f('&','hex')&&console.log(1)

Script & (otherwise known as Script B) - 62 characters

eval(require('fs').readFileSync('|','utf8').replace(/&/g,'|'))

Usage

# \| is Script A
# \& is Script B

$> echo "foo" | node \| 
$> cat \& | node \| 
1
$> echo "foo" | node \& 
1
$> cat \| | node \&

Description

Script B reads the contents of Script A and evals it after swapping the file names and the and operator to an or.

I named the files & and | so I can perform a single replace in Script B.

Answer 11

bash/grep — 59 chars

51 chars if we only count the actual program string.

$ a='grep -cx "$b" | grep -x 1'
$ b='grep -vcx "$a" | grep -x 1'
$ echo 'foo' | eval $a
$ echo $b | eval $a
1
$ echo 'foo' | eval $b
1
$ echo $a | eval $b

Answer 12

R (62 chars)

i=identical
A=function(x)if(i(x,B))1
B=function(x)if(!i(x,A))1

produces:

> A(123)
> A(A)
> A(B)
[1] 1
> B(123)
[1] 1
> B(A)
> B(B)
[1] 1

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Meta comment: R fairs relatively bad on code golf as there is no shortcut to function...