hdu3518

题解：

后缀数组

枚举长度为k(1<=k<=len/2)的满足要求的子串个数

代码：

#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;
typedef long long ll;
const int N=1010;
char str[N];
int wa[N],wb[N],wv[N],Ws[N],sa[N],Rank[N],height[N];
int cmp(int *r,int a,int b,int l)
{
    return r[a]==r[b]&&r[a+l]==r[b+l];
}
void da(const char *r,int *sa,int n,int m) 
{
    int *x=wa,*y=wb,*t;
    for (int i=0;i<m;i++) Ws[i]=0;
    for (int i=0;i<n;i++) Ws[x[i]=r[i]]++;
    for (int i=1;i<m;i++) Ws[i]+=Ws[i-1];
    for (int i=n-1;i>=0;i--) sa[--Ws[x[i]]]=i;
    for (int j=1,p=1;p<n;j*=2,m=p)
     {
         p=0;
        for (int i=n-j;i<n;i++) y[p++]=i;
        for (int i=0;i<n;i++)
         if (sa[i]>=j) y[p++]=sa[i]-j;
        for (int i=0;i<n;i++) wv[i]=x[y[i]];
        for (int i=0;i<m;i++) Ws[i]=0;
        for (int i=0;i<n;i++) Ws[wv[i]]++;
        for (int i=1;i<m;i++) Ws[i]+=Ws[i-1];
        for (int i=n-1;i>=0;i--) sa[--Ws[wv[i]]]=y[i];
        swap(x,y);x[sa[0]]=0;p=1;
        for (int i=1;i<n;i++)x[sa[i]]=cmp(y,sa[i-1],sa[i],j)?p-1:p++;
     }
    return;
}
void calheight(const char *r,int *sa,int n)
{
    int j,k=0;
    for (int i=1;i<=n;i++) Rank[sa[i]]=i;
    for (int i=0;i<n;height[Rank[i++]]=k)
     for (k?k--:0,j=sa[Rank[i]-1];r[i+k]==r[j+k];k++);
    return;
}
int solve(int k,int len)
{
    int maxx=0,minn=INT_MAX,ans=0;
    for (int i=1;i<=len;i++)
     {
        if (height[i]>=k)
         maxx=max(maxx,max(sa[i-1],sa[i])),minn=min(minn,min(sa[i-1],sa[i]));
         else
          {
            if (maxx-minn>=k) ans++;
            maxx=0,minn=INT_MAX;
          }
     }
    if (maxx-minn>=k)ans++;
    return ans;
}
int main()
{
    while (~scanf("%s",str) && strcmp(str,"#")!=0)
     {
        int len=strlen(str);
        da(str,sa,len+1,130);
        calheight(str,sa,len);
        ll ans=0;
        for (int i=1;i<=len/2;i++)ans+=solve(i,len);
        printf("%d
",ans);
     }
    return 0;
}