poj_1743_Musical Theme(后缀数组)

 1 #include<cstdio>
 2 #include<algorithm>
 3 #define F(i,a,b) for(int i=a;i<=b;i++)
 4 using namespace std;
 5 
 6 namespace suffixarray{    
 7     #define FN(n) for(int i=0;i<n;i++)
 8     const int N =2E4+7;
 9     int rnk[N],sa[N],height[N],c[N],s[N];
10     void getsa(int n,int m,int *x=rnk,int *y=height){
11         FN(m)c[i]=0;FN(n)c[x[i]=s[i]]++;FN(m)c[i+1]+=c[i];
12         for(int i=n-1;i>=0;i--)sa[--c[x[i]]]=i;
13         for(int k=1,p;p=0,k<=n;k=p>=n?N:k<<1,m=p){
14             for(int i=n-k;i<n;i++)y[p++]=i;
15             FN(n)if(sa[i]>=k)y[p++]=sa[i]-k;
16             FN(m)c[i]=0;FN(n)c[x[y[i]]]++;FN(m)c[i+1]+=c[i];
17             for(int i=n-1;i>=0;i--)sa[--c[x[y[i]]]]=y[i];
18             swap(x,y),p=1,x[sa[0]]=0;
19             for(int i=1;i<n;i++)
20             x[sa[i]]=y[sa[i-1]]==y[sa[i]]&&y[sa[i-1]+k]==y[sa[i]+k]?p-1:p++;
21         }
22         FN(n)rnk[sa[i]]=i;
23         for(int i=0,j,k=0;i<n-1;height[rnk[i++]]=k)
24         for(k=k?k-1:k,j=sa[rnk[i]-1];s[i+k]==s[j+k];k++);
25     }
26 }
27 
28 using namespace suffixarray;
29 int n;
30 inline void upd(int &a,int b){if(a>b)a=b;}
31 inline void upu(int &a,int b){if(a<b)a=b;}
32 
33 inline bool check(int x)
34 {
35     int l=N,r=0;
36     F(i,1,n)
37     {
38         if(height[i]>=x)
39         {
40             upd(l,sa[i]),upu(r,sa[i]);
41             if(r-l>=x)return 1;
42         }else l=r=sa[i];
43     }
44     return 0;
45 }
46 
47 int main()
48 {
49     while(scanf("%d",&n),n)
50     {
51         F(i,0,n-1)scanf("%d",s+i);
52         if(n<10){puts("0");continue;}
53         F(i,0,n-2)s[i]=s[i+1]-s[i]+89;
54         s[--n]=0,getsa(n+1,200);
55         int l=4,r=n,mid;
56         while(l<=r)mid=(l+r)>>1,check(mid)?l=mid+1:r=mid-1;
57         printf("%d\n",l<5?0:l);
58     }
59     return 0;
60 }