Given a string containing uppercase characters (A-Z), compress repeated 'runs' of the same character by storing the length of that run, and provide a function to reverse the compression. The output can be anything, as long as you can recreate the input with it.

Example:

: Input:  <code>WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW</code>
: Output: <code>12W1B12W3B24W1B14W</code>

Note: the encoding step in the above example is the same as a step of the [[Look-and-say sequence]].