求助：WA3个点on 1、3、8

#include<bits/stdc++.h>
using namespace std;
int d1[514514],d2[514514];
string s;
int n;
int main(){
    cin>>n;
    cin>>s;
    for(int i=0,l=0,r=-1;i<n;i++){
        int k;
        if(i>r){
            k=0;
        }
        else{
            k=min(d2[l+r-i+1],r-i+1);
        }
        while(i-k-1>=0&&i+k<n&&i+k<n&&s[i-k-1]==s[i+k]){
            k++;
        }
        d2[i]=k;
        k--;
        if(i+k>r){
            l=i-k-1;
            r=i+k;
        }
    }int cnt=0;
    int ans=0;
    for(int i=0;i<n;i++){
        if(d2[i]!=0&&d2[i]%2==0){
            if(i-d2[i]/2>=0)
            if(d2[i-d2[i]/2]==d2[i]/2){
                ans=max(ans,d2[i]*2);
            }
        }
    }
    cout<<ans;
    return 0;
}