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- #include <iostream>
- using namespace std;
- int main() {
- int n;
- cin >> n;
- string s;
- string sn = "";
- cin >> s;
- for(int i = n - 1; i >= 0; i--){
- sn += s[i];
- }
- const int p = 31;
- int hashsn = 0;
- long long p_pow = 1;
- for (char i : sn) { // хэщ перевернутой строки
- hashsn = int(((long long)hashsn + (i - 'a' + 1) * p_pow) % int(1e9 + 7));
- p_pow = p_pow * p;
- if(p_pow > 1e9) p_pow = 31;
- }
- int pn = 0;
- int hashs= 0;
- p_pow = 1;
- for (char i : s) { // хэш исходной строки
- pn = p_pow;
- hashs = int(((long long)hashs + (i - 'a' + 1) * p_pow) % int(1e9 + 7));
- p_pow = (p_pow * p) % int(1e9 + 7);
- }
- //int h = hashs;
- for(int i = 0; i < n; i++){
- if(i != 0){
- hashs = (hashs - s[i - 1] + 'a' - 1) / p; // находим хэш циклического сдвига на 1 символ
- hashs += pn * (s[i - 1] - 'a' + 1);
- }
- if(hashs == hashsn){
- cout << i;
- return 0;
- }
- }
- cout << -1;
- return 0;
- }
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