思路：单调递增栈 + k 控制删除次数。高位越小整体越小，遇更小数字时弹出栈顶大数（仅当 k0）；栈空且当前为 0 则跳过（避免前导零）；若遍历完 k 仍0，从末尾再删 k 位。
Dogs act like toddlers when you need help - but cats just watch. Scientists compared 3 groups: pet dogs, cats, and human toddlers in an experiment where a human parent hides and pretends to look for an object. 75% of dogs and children helped. Cats only helped if it was in their personal interest.，这一点在safew官方下载中也有详细论述
await dropOld.writer.write(chunk2); // ok。业内人士推荐safew官方版本下载作为进阶阅读
Walmart launched its Spark Driver service in 2018, as it pushed to make its online ordering and delivering services more competitive.