* Code should be very well commented: things must be explained in terms that even people not well versed with certain Z80 or Spectrum internals details should understand.
描述：给定字符串 num（非负整数）和整数 k，移除 k 位数字，使剩余数字最小。以字符串形式返回（不含前导零）。
。WPS下载最新地址对此有专业解读
Diglett Underground
1. 选基准：随机选一个元素作为基准(pivot)