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OI-codes/S2OJ/1970/1970.cpp

57 lines
1.3 KiB
C++

#include <iostream>
using std::cin;
using std::cout;
const char endl = '\n';
const int N = 1e5 + 5;
const int mod = 1e9 + 7;
int n, m, a[N], b[N];
long long ans1, ans2, ans3;
long long binpow(long long a, long long b, long long mod = ::mod) {
a %= mod;
long long res = 1;
while (b) {
if (b & 1) res = res * a % mod;
a = a * a % mod;
b >>= 1;
}
return res;
}
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> m;
for (int i = 1; i <= n; i++) {
cin >> a[i];
b[n - i + 1] = a[i];
}
long long x = binpow(2, m - 1);
for (int i = 1; i <= n; i++) {
ans1 = (((ans1 + static_cast<long long>(a[i]) * ((static_cast<long long>(x + 1) * n - i + 1) % mod + mod % mod) % mod * x) % mod) + mod) % mod;
}
for (int i = 1; i <= n; i++) {
ans2 = (((ans2 + static_cast<long long>(b[i]) * ((static_cast<long long>(x + 1) * n - i + 1) % mod + mod % mod) % mod * x) % mod) + mod) % mod;
}
for (int i = 1; i <= n; i++) {
ans3 = (((ans3 + static_cast<long long>(a[i]) * ((static_cast<long long>(x) * n - i + 1) % mod + mod % mod) % mod * x) % mod) + mod) % mod;
}
cout << std::max(((ans1 + ans3) % mod + mod) % mod, ((ans2 + ans3) % mod + mod) % mod) << endl;
return 0;
}