欧拉函数的线性筛法

Euler's-Totient-Function-Sieve(Linear).cpp

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+#include <cstdio>
+
+#define MAX_ELEMENT 100000000
+
+using namespace std;
+
+int prime[MAX_ELEMENT], pc, div[MAX_ELEMENT], phi[MAX_ELEMENT];
+
+void sieve(int n)
+{
+	phi[1] = 1;
+	for (int i = 2; i <= n; i++)
+	{
+		if (div[i] == 0)
+		{
+			prime[pc++] = i;
+			div[i] = i;
+			phi[i] = i - 1;
+		}
+		for (int j = 0; j < pc; j++)
+		{
+			if (i * prime[j] > n) break;
+			div[i * prime[j]] = prime[j];
+			if (i % prime[j] == 0)
+			{
+				phi[i * prime[j]] = phi[i] * prime[j];
+				break;
+			}
+			else
+			{
+				phi[i * prime[j]] = phi[i] * (prime[j] - 1);
+			}
+		}
+	}
+}
+
+int main()
+{
+	int n;
+	scanf("%d", &n);
+	sieve(n);
+	for (int i = 1; i <= n; i++)
+	{
+		printf("phi(%d) = %d\n", i, phi[i]);
+	}
+	return 0;
+}