Array splitting (regular thinking

Add link description

#include <bits/stdc++.h>
using namespace std;
map<string, bool> vis;
int ans = 1;
#define int long long
typedef  long long ll;
string to(string s, int a, int b)
{
    
    string ne = s;
    ne += '0' + a;
    ne += '0' + b;
    return ne;
}
void bfs(int n)
{
    
    queue<string> q;
    q.push("88");
    while (q.size())
    {
    
        auto x = q.front();
        q.pop();
        if (vis[x] == 1)
            continue;
            vis[x]=1;
            ans++;
            cout<<x<<endl;
        string c;
        for (int i = 0; i < x.size(); i++)
        {
    
            if (x[i] != '1')
            {
    
                int p = x[i] - '0';
                int a = p / 2, b = p - p / 2;
                string ne = to(c, a, b);
                if (i + 1 < x.size())
                    ne += x.substr(i + 1);
                if (vis.find(ne)==vis.end())
                {
    
                    q.push(ne);
                   
             
                }
                if (a != b)
                {
    
                    swap(a, b);
                    string mc = to(c, a, b);
                    if (i + 1 < x.size())
                        mc += x.substr(i + 1);
                    if (vis.find(mc)==vis.end())
                    {
    
                        
                        q.push(mc);
                        
                       
                    }
                }
            }
            c += x[i];
        }
    }
}
signed main()
{
    
    int n=1152921504606846976,mod=1e9+7;
    // cin >> n;
    // bfs(n);
    // cout<<"---"<<ans<<endl;
    int p=2;
    for(int i=4;i<=n;i*=2){
    
        p=(p*p+1)%mod;
        if(i==n)break;
    }
    cout<<p<<endl;
    return 0;
}