BZOJ 4052: [Cerc2013]Magical GCD

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cmath>
 4 #define N 300010
 5 using namespace std;
 6 int n,i,Log[N],j,l,left,right,mid;
 7 long long s[N][20],ans;
 8 long long gcd(long long a,long long b)
 9 {
10     if (b==0) return a;
11     return gcd(b,a%b);
12 }
13 long long Q(int l,int r)
14 {
15     int k=Log[r-l+1];
16     return gcd(s[l][k],s[r-(1<<k)+1][k]);
17 }
18 int main()
19 {
20     int test;
21     scanf("%d",&test);
22     while (test--)
23     {
24     ans=0;
25     scanf("%d",&n);
26     for (i=1;i<=n;i++)
27     scanf("%lld",&s[i][0]);
28     for (i=1;i<=n;i++)
29     Log[i]=log2(i);
30     for (i=n;i>=1;i--)
31     for (j=1;j<=Log[n];j++)
32     s[i][j]=gcd(s[i][j-1],s[i+(1<<(j-1))][j-1]);
33     
34     for (i=1;i<=n;i++)
35     {
36         l=i;
37         while (l<=n)
38         {
39             left=l;
40             right=n;
41             while (left<=right)
42             {
43                 mid=(left+right)>>1;
44                 if (Q(i,mid)==Q(i,l))
45                 left=mid+1;
46                 else
47                 right=mid-1;
48             }
49             l=right+1;
50             ans=max(ans,(right-i+1)*Q(i,right));
51         }
52     }
53     printf("%lld\n",ans);
54     }
55 }