View difference between Paste ID: eirSs36X and R76iqNQm

 #include<bits/stdc++.h>
 using namespace std;
 
 struct HashString
 {
   const int BASE = 1e9 + 7;
   const int P = 127;
 
   string s;
   size_t n;
 
   vector<int> power;
   vector<int> phash;
 
   HashString(string ps): s(ps), n(ps.size()) { init(); }
 
   void init()
   {
     phash.assign(n + 1, 0);
     power.assign(n + 1, 1);
     for(size_t i=1; i<=n; ++i)
     {
       phash[i] = (1LL * phash[i-1] * P + s[i-1]) % BASE;
       power[i] = (1LL * power[i-1] * P) % BASE;
     }
   }
 
   /** hash, power */
   inline pair<int, size_t> sub_hash(int i, int j)
   {
     return { phash[j+1] - phash[i], j - i };
   }
 };
 
 bool isPrime(int x)
 {
   int p=2;
   while(p * p <= x && x % p != 0) ++p;
   return ( x > 1 && p * p > x );
 }
 
 int max_len_preifx(const HashString &s1, const HashString &s2)
 {
   int left = 0, right = min(s1.n, s2.n) + 1;
   while (right - left > 1)
   {
     int mid = (left + right) / 2;
     if ( s1.phash[mid] == s2.phash[mid] )
       left = mid;
     else
       right = mid;
   }
   return left;
 }
 
 int main()
 {
   #ifdef AZHUKOV
   freopen("input.txt", "r", stdin);
   #endif // AZHUKOV
 
   string s;
   cin >> s;
   HashString s1(s);
   reverse(s.begin(), s.end());
   HashString s2(s);
   int n = s1.n;
 
   int ans = 0;
   for(int i=1; i<n-1; ++i)
   {
     /** чётная длина */
     int h1, h2, p1, p2;
     tie(h1, p1) = s2.sub_hash(n-1-i+1, n-1);
     tie(h2, p2) = s1.sub_hash(i, n-1);
 
 
 
   }
 }