'commit'

TangDou/AcWing_TiGao/T5/OuLaHanShu/201_EulerShai_YouHua.cpp

@@ -0,0 +1,44 @@
+#include <bits/stdc++.h>
+using namespace std;
+#define int long long
+#define endl "\n"
+const int N = 1010;
+
+// 筛法求欧拉函数
+int primes[N], cnt;
+bool st[N];
+int phi[N];
+int s[N];
+void euler(int n) {
+    phi[1] = 1;
+    for (int i = 2; i <= n; i++) {
+        if (!st[i]) {
+            primes[cnt++] = i;
+            phi[i] = i - 1;
+        }
+        for (int j = 0; primes[j] * i <= n; j++) {
+            st[i * primes[j]] = true;
+            if (i % primes[j] == 0) {
+                phi[i * primes[j]] = phi[i] * primes[j];
+                break;
+            }
+            phi[i * primes[j]] = phi[i] * (primes[j] - 1);
+        }
+    }
+}
+
+signed main() {
+    // 利用筛法，预处理出欧拉函数值数组
+    euler(N - 1); // 这里注意一下是N-1,防止数组越界
+
+    // 前缀和优化版本
+    for (int i = 1; i < N; i++) s[i] = s[i - 1] + phi[i];
+
+    int n, m;
+    cin >> m;
+    for (int i = 1; i <= m; i++) {
+        cin >> n;
+        printf("%d %d %d\n", i, n, s[n] * 2 + 1);
+    }
+    return 0;
+}