POJ3974：Palindrome——题解

#include<cstdio>
#include<cstring>
#include<algorithm>
#define N 1000010
using namespace std;
int l,cnt,mx,id,p[2*N],maxn;
char s[2*N];
int main(){
    while(233){
    cnt++;
    scanf("%s",s+1);
    if(s[1]==‘E‘&&s[2]==‘N‘&&s[3]==‘D‘)break;
    
    l=strlen(s+1);
    s[0]=‘@‘;
    for(int i=l;i>=1;i--)s[i*2]=s[i];
    for(int i=1;i<=2*l+1;i+=2)s[i]=‘#‘;
    s[2*l+2]=‘?‘;
    l=2*l+1;
    
    maxn=mx=0;
    for(int i=1;i<=l;i++){
        if(mx>i)p[i]=min(p[2*id-i],mx-i);
        else p[i]=1;
        while(s[i-p[i]]==s[i+p[i]])p[i]++;
        if(i+p[i]>mx){
        mx=i+p[i];
        id=i;
        }
        maxn=max(maxn,p[i]);
    }
    
    printf("Case %d: %d\n",cnt,maxn-1);
    }
    return 0;
}