Assuming this is a variant of RLE-style compression, the implementation is also wrong, if the input is `aabbcccddaa`, it will return "a4b2c3d2" instead of "a2b2

Assuming this is a variant of RLE-style compression, the implementation is also wrong, if the input is `aabbcccddaa`, it will return "a4b2c3d2" instead of "a2b2cc3d2a2".