POJ 3294 Life Forms(后缀数组)

题目链接:http://poj.org/problem?id=3294

题意:给定n个字符串,求出一个尽可能长的子串,使得该子串至少出现在n/2+1个给定的串中。

思路:将n个字符串连起来,二分答案,将后缀分成若干组,判断每组的后缀是否出现在不小于n/2+1个原串中。







int r[N],sa[N],wa[N],wb[N],wd[N],rank[N],h[N];





int cmp(int *r,int a,int b,int L)

{

    return r[a]==r[b]&&r[a+L]==r[b+L];

}





void da(int *r,int *sa,int n,int m)

{

    int i,j,p,*x=wa,*y=wb,*t;

    FOR0(i,m) wd[i]=0;

    FOR0(i,n) wd[x[i]=r[i]]++;

    FOR1(i,m-1) wd[i]+=wd[i-1];

    FORL0(i,n-1) sa[--wd[x[i]]]=i;

    for(j=1,p=1;p<n;j<<=1,m=p)

    {

        p=0;

        FOR(i,n-j,n-1) y[p++]=i;

        FOR0(i,n) if(sa[i]>=j) y[p++]=sa[i]-j;

        FOR0(i,m) wd[i]=0;

        FOR0(i,n) wd[x[i]]++;

        FOR1(i,m-1) wd[i]+=wd[i-1];

        FORL0(i,n-1) sa[--wd[x[y[i]]]]=y[i];

        t=x;x=y;y=t;p=1;x[sa[0]]=0;

        FOR1(i,n-1) x[sa[i]]=cmp(y,sa[i-1],sa[i],j)?p-1:p++;

    }

}







void calHeight(int *r,int *sa,int n)

{

    int i,j,k=0;

    FOR1(i,n) rank[sa[i]]=i;

    FOR0(i,n)

    {

        if(k) k--;

        j=sa[rank[i]-1];

        while(i+k<n&&j+k<n&&r[i+k]==r[j+k]) k++;

        h[rank[i]]=k;

    }

}



char s[N];

int n,b[N],M;

int ans[N],ansNum;





int OK(int mid)

{

    ansNum=0;

    int i,j,k,t,x,hash[105],L,R;

    FOR1(i,M)

    {

        L=i;

        while(L<=M&&h[L]<mid) L++;

        R=L;

        while(R<=M&&h[R]>=mid) R++;

        x=0; clr(hash,0);

        for(k=L-1;k<R;k++)

        {

            t=b[sa[k]];

            if(t&&!hash[t]) hash[t]=1,x++;

        }

        if(x>=n/2+1) ans[ansNum++]=sa[L-1];

        i=R;

    }

    return ansNum;

}



void deal()

{

    int low=1,high=1000,mid,L;

    while(low<=high)

    {

        mid=(low+high)>>1;

        if(OK(mid)) low=mid+1;

        else high=mid-1;

    }

    if(OK(low)) L=low;

    else OK(high),L=high;

    if(!L)

    {

        puts("?");

        return;

    }

    int i,j,k;

    FOR0(i,ansNum)

    {

        k=ans[i];

        FOR0(j,L) putchar(r[k+j]-100);

        puts("");

    }

}



int main()

{

    bool tag=false;

    while(scanf("%d",&n),n)

    {

        if(!tag) tag=true;

        else puts("");

        int i,j,k,len=0;

        len=0;

        for(i=1;i<=n;i++)

        {

            scanf("%s",s);

            k=strlen(s);

            for(j=0;j<k;j++) r[len]=s[j]+100,b[len++]=i;

            if(i<n) r[len]=i,b[len++]=0;

        }

        r[len]=0;

        da(r,sa,len+1,250);

        calHeight(r,sa,len);

        M=len;

        deal();

    }

    return 0;

}

  

你可能感兴趣的:(form)