http://www.yyycode.cn/index.php/2020/07/06/poj1852%e8%9a%82%e8%9a%81%e7%ae%80%e5%
Ants
Time Limit: 1000MS Memory Limit: 30000K
Total Submissions: 21449 Accepted: 8793
Description
An army of ants walk on a horizontal pole of length l cm, each with a constant speed of 1 cm/s. When a walking ant reaches an end of the pole, it immediatelly falls off it. When two ants meet they turn back and start walking in opposite directions. We know the original positions of ants on the pole, unfortunately, we do not know the directions in which the ants are walking. Your task is to compute the earliest and the latest possible times needed for all ants to fall off the pole.
Input
The first line of input contains one integer giving the number of cases that follow. The data for each case start with two integer numbers: the length of the pole (in cm) and n, the number of ants residing on the pole. These two numbers are followed by n integers giving the position of each ant on the pole as the distance measured from the left end of the pole, in no particular order. All input integers are not bigger than 1000000 and they are separated by whitespace.
Output
For each case of input, output two numbers separated by a single space. The first number is the earliest possible time when all ants fall off the pole (if the directions of their walks are chosen appropriately) and the second number is the latest possible such time.
Sample Input
2
10 3
2 6 7
214 7
11 12 7 13 176 23 191
Sample Output
4 8
38 207
Source
題意概括：
有n只螞蟻在木棍上爬行，每隻螞蟻的速度都是每秒1單位長度，現在給你所有螞蟻初始的位置（螞蟻運動方向未定），螞蟻相遇會掉頭反向運動，讓你求出所有螞蟻都·掉下木棍的最短時間和最長時間。
簡單說明一下爲什麼等價：
