https://github.com/wolframhwang/Revengers/blob/3c76c8db9de50060208644bc953bfa1c856e2337/%EC%95%8C%EA%B3%A0%EB%A6%AC%EC%A6%98/String%20Compression/string_compression_dolmac.cpp#L8 어허.. **You must write an algorithm that uses only constant extra space.** 공간복잡도가 상수입니다만
