POJ 1852 Ants

Ants

Time Limit: 1000MS		Memory Limit: 30000K
Total Submissions: 13879		Accepted: 6052

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

周练的一道题，当时感觉思路没错，运行结果也是对的，然而提交上去就是WA，纠结了半天。现在发现思路还是有点问题。

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
int main()
{
int i,j,k,l,m,n,t,a,sum1,sum2;
scanf("%d",&t);
while(t--)
{
scanf("%d%d",&l,&n);
sum1=sum2=0;
for(i=0;i<n;i++)
{
scanf("%d",&a);
sum1=max(sum1,min(l-a,a));
sum2=max(sum2,max(l-a,a));
}
printf("%d %d\n",sum1,sum2);
}
return 0;
}