題目：

思路：螞蟻相碰和不相碰的情況是一樣的，相當於交換位置繼續走。

代碼：

#include <iostream>
#include <cstdio>
#include <math.h> 
using namespace std;
typedef long long ll;

int main() {
    int t;
    int l,n;
    int key;
    int low,high;
    cin >> t;
    while(t--){
        cin >> l >> n;
        
 
int mn = 0;
        int mx = 0;
        for(int i = 0;i < n; i++){
            scanf("%d",&key);
            if(key < l/2){
                low = key;
                high = l-key;
            }else{
                low = l-key;
                high = key;
            }
            mn = max(low,mn);
            mx 
 
= max(high,mx);
        }
        cout << mn << " " << mx << endl;
    }
  return 0;
}
//  writen by zhangjiuding

POJ 1852 Ants O(n)