A look and say sequence is a self-descriptive sequence of integers first investigated by the mathematician John Horton Conway.

They are defined very simply. Start with an integer, say 1. Then we look at the integer and say it consists of one 1, and write this as 11, the next element in the sequence. Then we look at 11 and say that it consists of two 1's, or 21. Then 21 would be described as one 2 and one 1, or 1211. And so on.

The golf challenge is to write a program to print out the first 10 elements of a look and say sequence from a specified integer in the fewest number of keystrokes. The first 10 elements for the look and say sequence generated from the integer 1 are: 

@test = qw|1 11 21 1211 111221 312211 13112221 1113213211
           31131211131221 13211311123113112211|;

[download]

Here is a strawman solution that surely could be improved upon:

$s=1;print"$s\n";for(2..10){@n=split//,$s;my@r;$c=$n[0];$l=0;while(@n){$n=shift@n;if($n==$c){$l++}else{push@r,[$l,$c];$c=$n;$l=1;}}push@r,[$l,$c];$s =join"",map{"$_->[0]$_->[1]"}@r;print"$s\n";}

Bonus question: Can you find an integer that is its own look and say description?

-Mark

20050412 Edit by ysth: code tags

In reply to Golf: Look and Say Sequences by kvale

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