hdu 6025 Coprime Sequence (前后缀GCD)

 1 #include<bits/stdc++.h>
 2 #define F(i,a,b) for(int i=a;i<=b;++i)
 3 using namespace std;
 4 
 5 const int N=1e5+7;
 6 int t,pre[N],suf[N],n,a[N];
 7 
 8 int main()
 9 {
10     scanf("%d",&t);
11     while(t--)
12     {
13         scanf("%d",&n);
14         F(i,1,n)scanf("%d",a+i);
15         pre[1]=a[1],suf[n]=a[n];
16         F(i,2,n)pre[i]=__gcd(pre[i-1],a[i]);
17         for(int i=n-1;i>0;i--)suf[i]=__gcd(suf[i+1],a[i]);
18         int mx=0;
19         F(i,2,n-1)mx=max(mx,__gcd(pre[i-1],suf[i+1]));
20         mx=max(pre[n-1],mx),mx=max(suf[2],mx);
21         printf("%d\n",mx);
22     }
23     return 0;
24 }