POJ1743[Musical Theme]

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);


    }


}


 

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