✅

P5686 100pts

pre-sum/data.in

@@ -0,0 +1,3 @@
+3
+2 3 4
+3 4 5

pre-sum/main.cc

@@ -0,0 +1,30 @@
+#include <iostream>
+
+using namespace std;
+long long alpha[500005], beta[500005];
+long long pre_alpha[500005], pre_beta[500005];
+long long sum_alpha, sum_beta;
+long long ans;
+
+const int mod = 1000000007;
+
+int main() {
+    int n;
+    cin >> n;
+    for (int i = 1; i <= n; ++i) {
+        cin >> alpha[i];
+        pre_alpha[i] = (pre_alpha[i - 1] + alpha[i]) % mod;
+    }
+    for (int i = 1; i <= n; ++i) {
+        cin >> beta[i];
+        pre_beta[i] = (pre_beta[i - 1] + beta[i]) % mod;
+    }
+    for (int i = 1; i <= n; i++) {
+        (ans += (((n + 1) * pre_alpha[i]) % mod) * pre_beta[i]) %= mod;
+        sum_alpha = (sum_alpha + pre_alpha[i]) % mod;
+        sum_beta = (sum_beta + pre_beta[i]) % mod;
+    }
+    long long tot = (sum_alpha * sum_beta) % mod;
+    ans = (ans - tot + mod) % mod;
+    cout << ans;
+}