poj3974 最长回文串 exkmp

#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<cstring>

using namespace std;

int s[1000111];
int s1[1000111],s2[1000111],s3[1000111],s4[1000111];
int a[1000111],b[1000111],exEast[1000111],exWest[1000111];
int n,xzq,t;
char c;
bool p;

void Read()
{
    n=0;
    while(c=getchar(),(c<‘a‘||c>‘z‘)&&(c<‘A‘||c>‘Z‘));
    if(c==‘E‘)p=false;
    s[++n]=c;
    while(c=getchar(),c>=‘a‘&&c<=‘z‘)s[++n]=c;
}

void Exkmp(int *s1,int *s2,int n1,int n2)
{
    int len,k,i,l;
    len=0;
    for(i=2;i<=n1;i++){
        if(len<i){
            l=0;
            while(s1[i+l]==s1[1+l]&&i+l<=n1)l++;
            a[i]=l;
        }
        else{
            if(a[i-k+1]<len-i+1)a[i]=a[i-k+1];
            else{
                l=len-i+1;
                while(s1[i+l]==s1[1+l]&&i+l<=n1)l++;
                a[i]=l;
            }
        }
        if(i+a[i]-1>len){
            len=i+a[i]-1;
            k=i;
        }
    }
    len=0;
    for(i=1;i<=n2;i++){
        if(len<i){
            l=0;
            while(s2[i+l]==s1[1+l]&&i+l<=n2&&1+l<=n1)l++;
            b[i]=l;
        }
        else{
            if(a[i-k+1]<len-i+1)b[i]=a[i-k+1];
            else{
                l=len-i+1;
                while(s2[i+l]==s1[1+l]&&i+l<=n2&&1+l<=n1)l++;
                b[i]=l;
            }
        }
        if(i+b[i]-1>len){
            len=i+b[i]-1;
            k=i;
        }
    }
}

int Work(int l,int r)
{
    if(l==r)return 1;
    int mid=(l+r)/2;
    int x,z,q,i,n1,n2,k;
    x=0;
    z=0;
    q=0;
    x=Work(l,mid);
    z=Work(mid+1,r);
    if(x>z)q=x;
    else q=z;    
    n1=mid-l+1;
    for(i=l;i<=mid;i++){
        k=i-l+1;
        s1[k]=s[i];
        s3[n1-k+1]=s1[k];
    }
    n2=r-mid;
    for(i=mid+1;i<=r;i++){
        k=i-mid;
        s2[k]=s[i];
        s4[n2-k+1]=s2[k];
    }
    Exkmp(s3,s1,n1,n1);
    for(i=1;i<=n1;i++)exEast[i]=b[i];
    Exkmp(s2,s3,n2,n1);
    for(i=1;i<=n1;i++)exWest[n1-i+1]=b[i];
    exWest[0]=0;
    if(exWest[n1]*2>q)q=exWest[n1]*2;
    for(i=1;i<=n1;i++){
        if(exEast[i]*2>=n1-i+1){
            if(n1-i+1+exWest[i-1]*2>q)q=n1-i+1+exWest[i-1]*2;
        }
    }
    Exkmp(s3,s2,n1,n2);
    for(i=1;i<=n2;i++)exEast[i]=b[i];
    Exkmp(s2,s4,n2,n2);
    for(i=1;i<=n2;i++)exWest[n2-i+1]=b[i];
    if(exEast[1]*2>q)q=exEast[1]*2;
    exEast[n2+1]=0;
    for(i=1;i<=n2;i++){
        if(exWest[i]*2>=i){
            if(i+exEast[i+1]*2>q)q=i+exEast[i+1]*2;
        }
    }
    return q;
}

int main()
{
    p=true;
    t=0;
    while(true){
        t++;
        memset(s,0,sizeof(s));
        Read();
        if(p==false)break;
        xzq=Work(1,n);
        printf("Case %d: %d\n",t,xzq);
    }
}