P3773 [CTSC2017]吉夫特

https://www.luogu.com.cn/record/80299079

Luogu/P2398/P2398.cpp

@@ -0,0 +1,42 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n, phi[N];
+long long sum[N], ans;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    phi[1] = 1;
+    for (int i = 2; i <= n; i++) {
+        phi[i] = i;
+    }
+
+    for (int i = 2; i <= n; i++) {
+        if (phi[i] == i) {
+            for (int j = i; j < N; j += i) {
+                phi[j] = phi[j] / i * (i - 1);
+            }
+        }
+    }
+
+    for (int i = 1; i <= n; i++) {
+        sum[i] = sum[i - 1] + phi[i];
+    }
+
+    for (int i = 1; i <= n; i++) {
+        ans += (sum[n / i] * 2 - 1) * i;
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}

Luogu/P3773/P3773.cpp

@@ -0,0 +1,31 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 233333 + 5;
+const int mod = 1e9 + 7;
+
+int n, f[N], ans;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1, x; i <= n; i++) {
+        cin >> x;
+
+        for (int j = x - 1 & x; j; j = j - 1 & x) {
+            f[j] = (f[j] + f[x] + 1) % mod;
+        }
+
+        ans = (ans + f[x]) % mod;
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}

Luogu/P4071/P4071.cpp

@@ -0,0 +1,49 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e6 + 5;
+const int mod = 1e9 + 7;
+
+int t, n, m, fac[N], inv[N], fac_inv[N], d[N];
+
+inline int C(int n, int m) {
+    return static_cast<long long>(fac[n]) * fac_inv[m] % mod * fac_inv[n - m] % mod;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    fac[0] = 1;
+    for (int i = 1; i < N; i++) {
+        fac[i] = static_cast<long long>(fac[i - 1]) * i % mod;
+    }
+
+    inv[0] = inv[1] = 1;
+    for (int i = 2; i < N; i++) {
+        inv[i] = static_cast<long long>(mod - (mod / i)) * inv[mod % i] % mod;
+    }
+
+    fac_inv[0] = fac_inv[1] = 1;
+    for (int i = 2; i < N; i++) {
+        fac_inv[i] = static_cast<long long>(fac_inv[i - 1]) * inv[i] % mod;
+    }
+
+    d[2] = 1;
+    for (int i = 3; i < N; i++) {
+        d[i] = static_cast<long long>(i - 1) * (d[i - 1] + d[i - 2]) % mod;
+    }
+
+    cin >> t;
+
+    while (t--) {
+        cin >> n >> m;
+
+        cout << (n == m ? 1 : static_cast<long long>(d[n - m]) * C(n, m) % mod) << endl;
+    }
+
+    return 0;
+}