后缀数组。
CODE:
/*
AUTHOR: Su Jiao
DATE: 2010-7-23
DESCRIPTION:
$DESCRIPTION
*/
#include <stdio.h>
#include <string.h>
#define max(a,b) ((a)>(b)?(a):(b))
const int LOG2_MAXLENGTH=16;
const int MAXLENGTH=1<<LOG2_MAXLENGTH;
const int MAXALPHABET=1024;
typedef int string[MAXLENGTH];
int sort[max(MAXLENGTH,MAXALPHABET)];
int _SA[MAXLENGTH],_rank[MAXLENGTH],_TSA[MAXLENGTH],_Trank[MAXLENGTH];
int* SA=_SA;
int* rank=_rank;
int* TSA=_TSA;
int* Trank=_Trank;
void get_SA(string s,int length)
{
memset(sort,0,sizeof(sort));
for (int i=1;i<=length;i++) sort[s[i]]++;
for (int i=1;i<MAXALPHABET;i++) sort[i]+=sort[i-1];
for (int i=1;i<=length;i++) SA[sort[s[i]]–]=i;
rank[SA[1]]=1;
for (int i=2;i<=length;i++)
if (s[SA[i]]==s[SA[i-1]]) rank[SA[i]]=rank[SA[i-1]];
else rank[SA[i]]=rank[SA[i-1]]+1;
for (int block=1;block<length;block<<=1)
{
for (int i=1;i<=length;i++) sort[rank[SA[i]]]=i;
for (int i=length;i>=1;i–)
if (SA[i]-block>=1)
TSA[sort[rank[SA[i]-block]]–]=SA[i]-block;
for (int i=length-block+1;i<=length;i++)
TSA[sort[rank[i]]–]=i;
Trank[TSA[1]]=1;
for (int i=2;i<=length;i++)
if (rank[TSA[i]]==rank[TSA[i-1]]
&&rank[TSA[i]+block]==rank[TSA[i-1]+block])
Trank[TSA[i]]=Trank[TSA[i-1]];
else Trank[TSA[i]]=Trank[TSA[i-1]]+1;
int* swap;
swap=SA,SA=TSA,TSA=swap;
swap=rank,rank=Trank,Trank=swap;
}
}
int height[MAXLENGTH];
void get_height(string s,int length)
{
for (int h=0,i=1;i<=length;i++)
{
if (h) h–;
if (rank[i]!=1)
{
int j=SA[rank[i]-1];
while (s[i+h]==s[j+h]) h++;
}
height[rank[i]]=h;
}
}
int n,a,b;
string s;
bool check(int value)
{
#define abs(a) ((a)>=0?(a):-(a))
int i=1;
while (i<n)
{
while (i<n&&height[i]<value) i++;
int first=n,last=0;
if (i!=1) first=SA[i-1],last=SA[i-1];
while (i<n&&height[i]>=value)
{
if (SA[i]<first) first=SA[i];
if (SA[i]>last) last=SA[i];
i++;
}
if (last-first>=value) return true;
}
return false;
}
int main()
{
for (;;)
{
scanf(“%d”,&n);
if (!n) break;
scanf(“%d”,&b);
for (int i=1;i<n;i++)
a=b,scanf(“%d”,&b),s[i]=(MAXALPHABET>>1)+b-a;
s[n]=0;
get_SA(s,n-1);
get_height(s,n-1);
int L=0,R=n;
while (L+1!=R)
{
int mid=(L+R)>>1;
if (check(mid)) L=mid;
else R=mid;
}
if (L+1>=5) printf(“%d\n”,L+1);
else printf(“%d\n”,0);
}
}