不讲玛德的来了

#include<bits/stdc++.h>
using namespace std;
const long long mod = 1e9+7, N = 200009;
char s[N];
long long mul[N] = {1}, s1[N], s2[N], ans, mid;
int main()
{
    cin >> s + 1;
    for(int i = 1; s[i]; i++)
    {
        mul[i] = mul[i-1] * 26 % mod;
        s1[i] = (s1[i-1] + (s[i] - 'a') * mul[i]) % mod;
        s2[i] = (s2[i-1] + s[i] - 'a') * 26 % mod;
        mid = 1 + i >> 1;
        ans +=+ s1[i] == s2[i] && s1[mid] == s2[mid];
    }
    cout << ans;
}