UVA 1227 / Hashing

/***
 created: 2022-08-11-01.05.04
***/

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename U> using ordered_set=tree<U, null_type,less<U>,rb_tree_tag,tree_order_statistics_node_update>;
#define ll long long
#define ull unsigned long long
#define test int tt; cin>>tt; for(int cs=1;cs<=tt;cs++)
#define get_lost_idiot return 0
#define nl '\n'

ull p[1000005];
ull hash1[8][1000005];
ull base=307;

void power()
{
    p[0]=1;
    for(int i=1; i<=1000003; i++)
    {
        p[i]=p[i-1]*base;
    }
}

void hashing(string a,ll in)
{
    hash1[in][0]=0;
    for(int i=1; i<=a.size(); i++)
    {
        hash1[in][i]=(hash1[in][i-1]*base+a[i-1]);
    }
}

ull forwardhash(ll l,ll r,ll in)
{
    return (hash1[in][r] - (hash1[in][l-1] * p[r-l+1]));
}


int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    power();

    test
    {
        ll n,m,i,j,k,lo=1,hi=1e8,ans=0;

        cin>>n;

        vector<string>a(n+1);

        for(i=0; i<n; i++)
        {
            cin>>a[i];
            hashing(a[i],i);
            hi=min(hi,(ll)a[i].size());
        }


        while(lo<=hi)
        {
            ll mid=(lo+hi)>>1;

            unordered_set<ull>st;

            for(i=0; (i+mid-1)<a[0].size(); i++)
            {
                st.insert(forwardhash(i,i+mid-1,0));
            }

            for(i=1; i<n; i++)
            {
                unordered_set<ull>cur;

                for(j=0; (j+mid-1)<a[i].size(); j++)
                {
                    ull h1= forwardhash(j,j+mid-1,i);

                    if(st.find(h1)!=st.end())
                    {
                        cur.insert(h1);
                    }

                }

                st=cur;
            }

            if(st.size())
            {
                lo=mid+1;
                ans=mid;
            }
            else hi=mid-1;
        }

        cout<<ans<<nl;

    }

    get_lost_idiot;
}