Algorithm Interview: String Compression

Hi, here's your problem today. This problem was recently asked by Twitter:

Given an array of characters with repeats, compress it in place. The length after compression should be less than or equal to the original array.

Example:
Input: ['a', 'a', 'b', 'c', 'c', 'c']
Output: ['a', '2', 'b', 'c', '3']
Here's a starting point:

class Solution(object):

  def compress(self, chars):

    # Fill this in.



print Solution().compress(['a', 'a', 'b', 'c', 'c', 'c'])

# ['a', '2', 'b', 'c', '3']