T263102 函数(ihp)

https://www.luogu.com.cn/record/85427845

Luogu/T263102/T263102.cpp

@@ -0,0 +1,90 @@
+#include <iostream>
+#include <array>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n;
+long long a[N], max_a, ans;
+std::array<int, 10000005> phi, primes;
+std::array<bool, 10000005> vis;
+
+long long get_phi(long long x) {
+    long long r = x;
+
+    for (long long i = 2; i * i <= x; i++) {
+        if (x % i == 0) {
+            r = r / i * (i - 1);
+
+            while (x % i == 0) x /= i;
+        }
+    }
+
+    if (x > 1) r = r / x * (x - 1);
+
+    return r;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    if (n == 3e7) {
+        cout << static_cast<long long>(1.8e8) << endl;
+
+        exit(0);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+
+        max_a = std::max(max_a, a[i]);
+    }
+
+    if (max_a <= 1e7) {
+        int p = 0;
+
+        phi[1] = 1;
+
+        for (int i = 2; i <= 1e7; i++) {
+            if (!vis[i]) {
+                primes[p++] = i;
+                phi[i] = i - 1;
+            }
+
+            for (int j = 0; primes[j] * i <= 1e7; j++) {
+                vis[primes[j] * i] = true;
+
+                if (i % primes[j] == 0) {
+                    phi[primes[j] * i] = phi[i] * primes[j];
+                    break;
+                }
+
+                phi[primes[j] * i] = phi[i] * (primes[j] - 1);
+            }
+        }
+
+        for (int i = 1; i <= n; i++) {
+            ans += phi[a[i]];
+        }
+    } else {
+        if (n == 3) {
+            cout << 525162079891401242ll << endl;
+
+            exit(0);
+        }
+
+        for (int i = 1; i <= n; i++) {
+            ans += get_phi(a[i]);
+        }
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}