SPOJ题目687 Repeats（后缀数组+RMQ求重复次数最多的子串的重复次数）

REPEATS - Repeats

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A string s is called an (k,l)-repeat if s is obtained by concatenating k>=1 times some seed string t with length l>=1. For example, the string

s = abaabaabaaba

is a (4,3)-repeat with t = aba as its seed string. That is, the seed string t is 3 characters long, and the whole string s is obtained by repeating t 4 times.

Write a program for the following task: Your program is given a long string u consisting of characters ‘a’ and/or ‘b’ as input. Your program must find some (k,l)-repeat that occurs as substring within u with k as large as possible. For example, the input string

u = babbabaabaabaabab

contains the underlined (4,3)-repeat s starting at position 5. Since u contains no other contiguous substring with more than 4 repeats, your program must output the maximum k.

Input

In the first line of the input contains H- the number of test cases (H <= 20). H test cases follow. First line of each test cases is n - length of the input string (n <= 50000), The next n lines contain the input string, one character (either ‘a’ or ‘b’) per line, in order.

Output

For each test cases, you should write exactly one interger k in a line - the repeat count that is maximized.

Example

Input:117babbabaabaabaababOutput:4

since a (4, 3)-repeat is found starting at the 5th character of the input string.
ac代码

#include<stdio.h>         #include<string.h>         #include<algorithm>         #include<iostream>        #define min(a,b) (a>b?b:a)     #define max(a,b) (a>b?a:b)      using namespace std;        char str[53030];      int sa[53030],Rank[53030],rank2[53030],height[53030],c[53030],*x,*y,s[53030];    int n;    void cmp(int n,int sz)    {        int i;        memset(c,0,sizeof(c));        for(i=0;i<n;i++)            c[x[y[i]]]++;        for(i=1;i<sz;i++)            c[i]+=c[i-1];        for(i=n-1;i>=0;i--)            sa[--c[x[y[i]]]]=y[i];    }    void build_sa(char *s,int n,int sz)    {        x=Rank,y=rank2;        int i,j;        for(i=0;i<n;i++)            x[i]=s[i],y[i]=i;        cmp(n,sz);        int len;        for(len=1;len<n;len<<=1)        {            int yid=0;            for(i=n-len;i<n;i++)            {                y[yid++]=i;            }            for(i=0;i<n;i++)                if(sa[i]>=len)                    y[yid++]=sa[i]-len;                cmp(n,sz);            swap(x,y);            x[sa[0]]=yid=0;            for(i=1;i<n;i++)            {                if(y[sa[i-1]]==y[sa[i]]&&sa[i-1]+len<n&&sa[i]+len<n&&y[sa[i-1]+len]==y[sa[i]+len])                    x[sa[i]]=yid;                else                    x[sa[i]]=++yid;            }            sz=yid+1;            if(sz>=n)                break;        }        for(i=0;i<n;i++)            Rank[i]=x[i];    }    void getHeight(char *s,int n)    {        int k=0;        for(int i=0;i<n;i++)        {            if(Rank[i]==0)                continue;            k=max(0,k-1);            int j=sa[Rank[i]-1];            while(s[i+k]==s[j+k])                k++;            height[Rank[i]]=k;        }    }  int minv[53010][20],lg[53030];    void init_lg()  {      int i;      lg[1]=0;      for(i=2;i<52020;i++)      {          lg[i]=lg[i>>1]+1;      }  }  void init_RMQ(int n)  {      int i,j,k;      for(i=1;i<=n;i++)      {          minv[i][0]=height[i];      }      for(j=1;j<=lg[n];j++)        {            for(k=0;k+(1<<j)-1<=n;k++)            {                minv[k][j]=min(minv[k][j-1],minv[k+(1<<(j-1))][j-1]);             }        }  }  int lcp(int l,int r)  {      l=Rank[l];      r=Rank[r];      if(l>r)          swap(l,r);      l++;      int k=lg[r-l+1];      return min(minv[l][k],minv[r-(1<<k)+1][k]);    } int main(){int t;scanf("%d",&t);while(t--){int n;scanf("%d",&n);int i,j,k;for(i=0;i<n;i++){scanf("%s",str+i);}build_sa(str,n+1,128);getHeight(str,n);init_lg();init_RMQ(n);int maxn=0;for(i=1;i<n;i++){for(j=0;j+i<n;j+=i){int k=lcp(j,j+i);int now=k/i;int tj=j-(i-k%i);if(tj>=0){if(lcp(tj,tj+i)>=i-k%i)now++;}if(now>maxn)maxn=now;}}printf("%d\n",maxn+1);}}