题意：
There is a sequence of integers. Your task is to find the longest subsequence that satisfies the following condition: the difference between the maximum element and the minimum element of the subsequence is no smaller than m and no larger than k.
分析：找一个最长的区间满足区间内k>=最大值-最小值>=m。可以用两个单调队列，一个单增维护最小值，一个单减维护最大值