problem 11, modified run-length encoding
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If an element has no duplicates, mark it as such.

Example:

encodeModified "aaaabccaadeeee"

[Multiple 4 'a',Single 'b',Multiple 2 'c',
Multiple 2 'a',Single 'd',Multiple 4 'e']

problem 12, Decode a run-length encoded list.
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Given a run-length code list generated as specified in problem 11. Construct its uncompressed version.

Example:

decodeModified
[Multiple 4 'a',Single 'b',Multiple 2 'c',
Multiple 2 'a',Single 'd',Multiple 4 'e']

"aaaabccaadeeee"