Run-Length Encoding

sh - 33 29 28

read;echo`xargs -n1|uniq -c`

Usage:

$ cat input|sh 1015.sh
2 1 1 3 2 2

• read skips the first line

• xargs -n1 reads the reast and outputs each number on one line:

  1
  1
  3
  2
  2
  

• uniq -c filters adjacent matching lines (with the c switch it also prints the number of adjancent lines) :

  2 1
  1 3
  2 2
  

• echo sees those numbers as separate arguments and just prints them separated by a space:

  2 1 1 3 2 2
  

Perl, 46 56 68

$_=<>;s/(?{$a=1})(\d+)( \1(?{++$a}))*/$a $1/g

Run with the p command-line option (counted in code size):

$ perl -pe '$_=<>;s/(?{$a=1})(\d+)( \1(?{++$a}))*/$a $1/g'
5
1 1 3 2 2
  => 2 1 1 3 2 2
3
1 1 1
  => 3 1

Haskell (84 82)

import List
main=interact$unwords.(>>= \x->[show$length x,x!!0]).group.tail.words

Number of elements in the list is ignored.