We give the first algorithm for adaptive alphabetic prefix-free coding that is worst-case optimal in terms of time and compression when $σ\in o \left( \frac{n^{1 / 2}}{\log n} \right)$, where $σ$ is the size of the alphabet and $n$ is the length of the input.

翻译：我们提出了首个自适应字母表无前缀编码算法，当 $σ\in o \left( \frac{n^{1 / 2}}{\log n} \right)$ 时，该算法在时间与压缩性能上均达到最坏情况最优，其中 $σ$ 表示字母表大小，$n$ 为输入长度。