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OI-codes/Luogu/P5431/P5431.cpp

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#include <iostream>
using std::cin;
using std::cout;
const char endl = '\n';
const int N = 5e6 + 5;
int n, p, _k, k, a[N], b[N], s[N], ans;
int binpow(int a, int b) {
int res = 1;
while (b) {
if (b & 1) res = static_cast<long long>(res) * a % p;
a = static_cast<long long>(a) * a % p;
b >>= 1;
}
return res;
}
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> p >> _k;
s[0] = 1;
for (int i = 1; i <= n; i++) {
cin >> a[i];
s[i] = static_cast<long long>(s[i - 1]) * a[i] % p;
}
b[n + 1] = binpow(s[n], p - 2);
for (int i = n; i; i--) {
b[i] = static_cast<long long>(b[i + 1]) * a[i] % p;
}
k = _k;
for (int i = 1; i <= n; i++) {
ans = (ans + static_cast<long long>(s[i - 1]) * b[i + 1] % p * k) % p;
k = static_cast<long long>(k) * _k % p;
}
cout << ans << endl;
return 0;
}