URAL/1393

来自"NOCOW"

啊，依旧是后缀数组呢。

#include <cstdio>
#include <cstring>
const int maxn=500010;
int r[maxn],sa[maxn],rank[maxn],height[maxn];
int wa[maxn],wb[maxn],ws[maxn],wv[maxn];
char s[maxn];
bool cmp(int* r,int a,int b,int l)
{
    return (r[a] == r[b]) && (r[a+l] == r[b+l]);
}
void da(int n,int m)
{
    int i,j,p,*x=wa,*y=wb,*t;
    for (i=0;i<m;++i)  ws[i]=0;
    for (i=0;i<n;++i)  ++ws[x[i]=r[i]];
    for (i=1;i<m;++i)  ws[i]+=ws[i-1];
    for (i=n-1;i>=0;--i)  sa[--ws[x[i]]]=i;
    for (j=p=1;p<n;j<<=1,m=p)
    {
        for (p=0,i=n-j;i<n;++i)  y[p++]=i;
        for (i=0;i<n;++i)  if (sa[i] >= j)  y[p++]=sa[i]-j;
        for (i=0;i<n;++i)  wv[i]=x[y[i]];
        for (i=0;i<m;++i)  ws[i]=0;
        for (i=0;i<n;++i)  ++ws[wv[i]];
        for (i=1;i<m;++i)  ws[i]+=ws[i-1];
        for (i=n-1;i>=0;--i)  sa[--ws[wv[i]]]=y[i];
        for (t=x,x=y,y=t,p=1,x[sa[0]]=0,i=1;i<n;++i)
            x[sa[i]]=cmp(y,sa[i-1],sa[i],j)?p-1:p++;
    }
}
void calheight(int n)
{
    int i,j,k=0;
    for (i=1;i<=n;i++)  rank[sa[i]]=i;
    for (i=0;i<n;height[rank[i++]]=k)
    for (k?k--:0,j=sa[rank[i]-1];r[i+k]==r[j+k];k++);
}
int min(int a,int b)  {  return a>b?b:a;  }
int main()
{
    int i,n,now;
    double sum=0.0;
    scanf("%d%*c%s",&n,s);
    for (i=0;i<n;s[i+n]=s[i++]);
    for (i=0,n<<=1;i<=n;r[i]=s[i++]);
    da(n+1,256);
    calheight(n);
    for (i=1,now=(n>>1);i<=n;++i)
    {
        now=min(now,height[i]);
        if (sa[i] < (n>>1))
        {
            sum+=(double)now;
            now=(n>>1);
        }
    }
    printf("%.3lf\n",sum/(double)((n>>1)-1));
    return 0;
}
//by zzy