#include #include #include #include using namespace std; using i64 = long long; struct rolling_hash { rolling_hash(const string& s, const vector& mods, const vector& bases); i64 calc_hash(int l, int r); // [l, r]。つまりlもrも含む。1-indexed private: string s; vector> b, H; // b[2][s.size()+1], H[2][s.size()+1] vector mods, bases; }; template vector segment_sieve(Int a, Int b) { Int sqb = sqrt(b); vector is_prime_small(sqb+1, true); is_prime_small[0] = is_prime_small[1] = false; vector is_prime(b-a, true); is_prime[0] = a != 1; for(Int i=2; i*i res; for(Int i=0; i& mods, const vector& bases) : s(s), mods(mods), bases(bases) { b.resize(2); H.resize(2); int n = s.size(); i64 B; for(int j=0; j<2; ++j) { B = bases[j] % mods[j]; b[j].resize(n+1); H[j].resize(n+1); b[j][0] = 1; H[j][0] = 0; for(int i=0; i primes = segment_sieve(LO, HI); shuffle(begin(primes), end(primes), genrand); vector mods, bases; for(int i=0; i<2; ++i) { mods.push_back(primes[i]); bases.push_back(genrand()); } string s, t; cin >> s; int n = s.size(); t = s; reverse(begin(t), end(t)); rolling_hash rhs(s, mods, bases), rht(t, mods, bases); // dp[i] := iから最後までの回文の個数 vector dp(n+2, 0); // dp[n+2] for(int i=n; i>0; --i) { dp[i] = dp[i+1]; if(rhs.calc_hash(i, n) == rht.calc_hash(1, n+1-i)) { ++dp[i]; } } i64 res = 0; for(int i=1; i<=n; ++i) { if(rhs.calc_hash(1, i) != rht.calc_hash(n+1-i, n)) { continue; } for(int j=i+1; j+2<=n; ++j) { if(rhs.calc_hash(i+1, j) != rht.calc_hash(n+1-j, n-i)) { continue; } res += dp[j+2]; } } printf("%lld\n", res); return 0; }