bzoj2565: 最长双回文串

  
#include<cstdio> 
#include<iostream> 
#include<cstring> 
#include<cstdlib> 
#include<algorithm> 
#include<cmath> 
using namespace std; 
  
int p[210000],l[210000],r[210000]; 
char sc[110000],ss[210000]; 
int main() 
{ 
    scanf("%s",sc+1);int len=strlen(sc+1); 
    for(int i=1;i<=len;i++) 
        ss[2*i-1]='#', ss[2*i]=sc[i]; 
    ss[2*len+1]='#';len=2*len+1; 
      
    int k=0;p[k]=0; 
    for(int i=1;i<=len;i++) 
    { 
        int Lk=k-p[k]+1,Rk=k+p[k]-1; 
        int j=k-(i-k); 
          
        if(Lk<=j)p[i]=min(p[j],j-Lk+1); 
        else p[i]=0; 
          
        while(ss[i+p[i]]==ss[i-p[i]]&&i-p[i]>0&&i+p[i]<=len)p[i]++; 
        if(i+p[i]-1>Rk)k=i; 
    } 
      
    int mx=1; 
    for(int i=1;i<=len;i++) 
        while(mx<=i+p[i])l[mx++]=i; 
    mx=len; 
    for(int i=len;i>=1;i--) 
        while(mx>=i-p[i])r[mx--]=i; 
      
    int ans=0; 
    for(int i=1;i<=len;i++) 
        if(ss[i]=='#')ans=max(ans,(i-l[i])*2+(r[i]-i)*2+1); 
    printf("%d\n",ans/2); 
    return 0; 
}