求条

#include<bits/stdc++.h>
using namespace std;
#define int long long 
const int N=1e6+5;
const int base=114;
const int Mod=1e9+7;
int a[N];
int p[N];
int f(int y,int x)
{
    return (a[y]-a[x-1]*p[y-x+1]%Mod)%Mod;
}
signed main()
{
	cin.tie(0)->sync_with_stdio(0);
	string s;
    cin>>s;
    for(int i=1;i<=(int)s.size();i++) a[i]=(a[i-1]*base+(s[i-1]-'a'+1))%Mod;
    //for(int i=1;i<=(int)s.size();i++) cout<<a[i]<<" ";
    p[0]=1;
    for(int i=1;i<=(int)s.size();i++) p[i]=p[i-1]*base%Mod;
    int ans=0;
    for(int i=1;i<(int)s.size();i++)
    {
     //cout<<i<<":"<<endl;
        int l=1,r=i;
        int id=-1;
        //cout<<f(1,1)<<" "<<f(4,4)<<endl;
        while(l<=r)
        {
            int mid=l+r>>1;
            //cout<<mid<<" ";
            if(f(mid,1)!=f(s.size()+mid-i,s.size()-i+1))
            {
                r=mid-1;
                id=mid;
                
            }
            else l=mid+1;
        }
     //cout<<id<<endl;
        if(id==-1) ans=max(ans,i);
        else
        {
            //cout<<"114514 "<<id-1<<" "<<s.size()-i+id-1<<endl;
            l=id+1,r=i;
            int Id=-1;
            int L=l;
            while(l<=r)
            {
                int mid=l+r>>1;
                    //cout<<mid<<" "<<L<<" "<<s.size()<<" "<<s.size()-mid+L<<endl;
                if(f(mid,L)!=f(s.size()+mid-i,s.size()-i+L))
                {
                    r=mid-1;
                    Id=mid;
                }
                else l=mid+1;
            }
            //cout<<Id<<endl;
            if(Id==-1) ans=max(ans,i);
            else
            {
                if(Id==s.size()-i+id&&s[s.size()-i+Id-1]==s[id-1])
                {
                    l=Id+1,r=i;
                    Id=-1;
                    L=l;
                    while(l<=r)
                    {
                        int mid=l+r>>1;
                        if(f(mid,L)!=f(s.size()+mid-i,s.size()-i+L))
                        {
                            r=mid-1;
                            Id=mid;
                        }
                        else l=mid+1;
                    }
                    if(Id==-1) ans=max(ans,i);
                }
            }
        }
    }
    cout<<ans;
	return 0;
}