poj 3368 Frequent values

http://poj.org/problem?id=3368

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#define maxn 100100
using namespace std;

int a[maxn],f[maxn][30],n,q,x,y,b[maxn];

int main()
{
    while(scanf("%d",&n)!=EOF)
    {
        if(n==0) break;
        scanf("%d",&q);
        memset(f,0,sizeof(f));
        for(int i=1; i<=n; i++)
        {
            scanf("%d",&a[i]);
        }
        memset(b,0,sizeof(b));
        for(int i=1; i<=n; i++)
        {
            if(i==1)
            {
                b[1]=1;
                continue;
            }
            if(a[i]==a[i-1])
            {
                b[i]=b[i-1]+1;
            }
            else
                b[i]=1;
        }
        for(int i=1; i<=n; i++)
        {
            f[i][0]=b[i];
        }
        int m=(int)(log(n*1.0)/(log(2.0)));
        for(int j=1; j<=m; j++)
        {
            for(int i=1; i<=n; i++)
            {
                if(i+(1<<j)-1<=n)
                {
                    f[i][j]=max(f[i][j-1],f[i+(1<<(j-1))][j-1]);
                }
            }
        }
        for(int i=0; i<q; i++)
        {
            scanf("%d%d",&x,&y);
            int t=x;
            while(t<=y&&a[t]==a[t-1])
                t++;
            int k=(int)(log(y-t+1.0)/(log(2.0)));
            int c=max(f[t][k],f[y-(1<<k)+1][k]);
            if(t>y) c=0;
            printf("%d
",max(t-x,c));
        }
    }
    return 0;
}