求解原根

Primitive-Root.cpp

@@ -0,0 +1,45 @@
+#include <cstdio>
+
+typedef long long ll;
+
+using namespace std;
+
+ll p;
+
+ll qpow(ll x, ll y)
+{
+	if (y == 1) return x;
+	ll t = qpow(x, y >> 1);
+	t = t * t % p;
+	if ((y & 1) == 0) return t;
+	return t * x % p;
+}
+
+int main()
+{
+	ll x;
+	while (true)
+	{
+		scanf("%lld", &p);
+		for (ll k = 2; ; k++)
+		{
+			x = p - 1;
+			for (ll i = 2; i * i <= x; i++)
+			{
+				if (x % i == 0)
+				{
+					if (qpow(k, (p - 1) / i) == 1) goto NEXT;
+					while (x % i == 0) x /= i;
+				}
+			}
+			if (x != 1)
+			{
+				if (qpow(k, (p - 1) / x) == 1) goto NEXT;
+			}
+			printf("%lld\n", k);
+			break;
+		NEXT:;
+		}
+	}
+	return 0;
+}