#1970. 【Public NOIP Round #5】青鱼和序列

https://sjzezoj.com/submission/72550

S2OJ/1970/1970.cpp

@@ -0,0 +1,56 @@
+#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;
+}