设x1，x2，…xn是实直线上的n个点。用固定长度为k的闭区间覆盖这n个点，至少需要多少个这样的固定长度闭区间？设计此问题的有效算法。 -Set x1, x2, ... xn is a real line on the n points. Fixed length k, closed interval covering the n points, at least the number of such fixed-length closed interval? Design an effec