区间相交问题 给定 x 轴上 n 个闭区间。去掉尽可能少的闭区间，使剩下的闭区间都不相交。 算法设计： 对于给定的 n 个闭区间，计算去掉的最少闭区间数。-Given X axis n on a closed interval. Remove as much as possible closed interval less, so that the rest of the closed interval are disjoint.