HDU 6153A Secret（kmp）

A Secret

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 256000/256000 K (Java/Others)
Total Submission(s): 803    Accepted Submission(s): 315

Problem Description

Today is the birthday of SF,so VS gives two strings S1,S2 to SF as a present,which have a big secret.SF is interested in this secret and ask VS how to get it.There are the things that VS tell:
  Suffix(S2,i) = S2[i...len].Ni is the times that Suffix(S2,i) occurs in S1 and Li is the length of Suffix(S2,i).Then the secret is the sum of the product of Ni and Li.
  Now SF wants you to help him find the secret.The answer may be very large, so the answer should mod 1000000007.

 

Input

Input contains multiple cases.
  The first line contains an integer T,the number of cases.Then following T cases.
  Each test case contains two lines.The first line contains a string S1.The second line contains a string S2.
  1<=T<=10.1<=|S1|,|S2|<=1e6.S1 and S2 only consist of lowercase ,uppercase letter.

 

Output

For each test case,output a single line containing a integer,the answer of test case.
  The answer may be very large, so the answer should mod 1e9+7.

 

Sample Input

2aaaaaaaabababababa

 

Sample Output

1319
Hint
case 2: Suffix(S2,1) = "aba",Suffix(S2,2) = "ba",Suffix(S2,3) = "a".N1 = 3,N2 = 3,N3 = 4.L1 = 3,L2 = 2,L3 = 1.ans = （3*3+3*2+4*1）%1000000007.
 

 

Source

2017中国大学生程序设计竞赛 - 网络选拔赛

想法：

kmp变形

代码：

#include<cstdio>#include<iostream>#include<cstring>#include<algorithm>using namespace std;#define ll long longconst int mn=1e6+5;int n,m;int next1[mn];char s[mn],t[mn];ll id[mn];const int mod=1e9+7;void get_Next(){    int i=0,j=-1;    next1[0]=-1;    while(i<m)    {        if(j==-1||t[i]==t[j])            next1[++i]=++j;        else j=next1[j];    }}void KMP(){    int i=0,j=0;    while(i<n)    {        if(j==-1||s[i]==t[j])        ++i,++j;        else        j=next1[j];        id[j]++;        if(j==m)        j=next1[j];    }}int main(){    int T;    scanf("%d",&T);    while(T--)    {        memset(id,0,sizeof(id));        scanf("%s%s",s,t);        n=strlen(s),m=strlen(t);        reverse(s,s+n);        reverse(t,t+m);        get_Next();        KMP();        ll ans=0;        for(int i=m;i>0;i--)        {            id[next1[i]]+=id[i];            ans=(ans+id[i]*i)%mod;        }        printf("%lld\n",ans);    }    return 0;}

代码二：

exkmp

#include<iostream>#include<cstdio>#include<string>#include<cstring>#include<algorithm>using namespace std;typedef long long ll;const int mod = 1000000007;int cnt[1000005];inline ll Add(ll n){    ll m=((n%mod)*((n+1)%mod)/2)%mod;    return m;}char t[1000005],p[1000005];int Next[1000005],ex[1000005];void pre(char p[]){    int m=strlen(p);    Next[0]=m;    int j=0,k=1;    while(j+1<m&&p[j]==p[j+1]) j++;    Next[1]=j;    for(int i=2; i<m; i++)    {        int P=Next[k]+k-1;        int L=Next[i-k];        if(i+L<P+1) Next[i]=L;        else        {            j=max(0,P-i+1);            while(i+j<m&&p[i+j]==p[j]) j++;            Next[i]=j;            k=i;        }    }}void exkmp(char p[],char t[]){    int m=strlen(p),n=strlen(t);    pre(p);    int j=0,k=0;    while(j<n&&j<m&&p[j]==t[j]) j++;    ex[0]=j;    for(int i=1;i<n;i++)    {        int P=ex[k]+k-1;        int L=Next[i-k];        if(i+L<P+1) ex[i]=L;        else        {            j=max(0,P-i+1);            while(i+j<n&&j<m&&t[i+j]==p[j]) j++;            ex[i]=j;            k=i;        }    }}int main(){    int ss;    scanf("%d",&ss);    while(ss--)    {        scanf("%s %s",&t,&p);        int Ti=strlen(t);        int Pi=strlen(p);        reverse(t,t+Ti);        reverse(p,p+Pi);        pre(p);        memset(Next, 0,sizeof(Next));        memset(ex, 0, sizeof(ex));        exkmp(p,t);        ll ans=0;        for(int i=0; i<Ti;++i)        {            if(ex[i])            {                //printf("%d\t",ex[i]);               ans=(ans+Add(ex[i])%mod)%mod;            }        }       printf("%d\n",ans%mod);    }    return 0;}