Message patterns can also be refined using #with: message:
* @param n 数组长度
，详情可参考heLLoword翻译官方下载
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）。
Cluster & Border Point Definition: The map is divided into clusters, and border points are identified using the Ford-Fulkerson based method.