求助

#include <bits/stdc++.h>
using namespace std;
char b[11000005],a[22000005];
int p[22000005];
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);
    cin>>b;
    a[0]='^',a[1]='#';
    int pp=2;
    for(int i=0;i<strlen(b);i++){
        a[pp]=b[i],a[pp+1]='#';
        pp+=2;
    }
    a[pp]='$',a[pp+1]='\0';
    int c=0,r=0,ans=0,len=strlen(a);
    for(int i=1;i<len;i++){
        if(i<r){
            int i_mirror=2*c-i;
            p[i]=min(r-i,p[i_mirror]);
        }
        while(a[i+(p[i]+1)]==a[i-(p[i]+1)]){
            p[i]++;
        }
        if(i+p[i]>r){
            c=i,r=i+p[i];
        }
        ans=max(ans,p[i]);
    }
    cout<<ans;
}