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problem-69.c

@@ -0,0 +1,60 @@
+#include <stdio.h>
+
+unsigned int gcd(unsigned int u, unsigned int v)
+{
+	int shift;
+	if (u == 0) return v;
+	if (v == 0) return u;
+	shift = __builtin_ctz(u | v);
+	u >>= __builtin_ctz(u);
+	do {
+		v >>= __builtin_ctz(v);
+		if (u > v) {
+			unsigned int t = v;
+			v = u;
+			u = t;
+		}
+		v = v - u;
+	} while (v != 0);
+	return u << shift;
+}
+
+
+unsigned int is_coprime(unsigned int u, unsigned int v)
+{
+	if (gcd(u, v) == 1)
+		return 1;
+	return 0;
+}
+
+
+int main(int argc, char** argv) {
+	unsigned int i, j;
+	unsigned int coprimes;
+	unsigned int MAX_NUM = 1000000;
+	int greatest = 0;
+	double ratio = 0;
+
+	for (i=1; i<MAX_NUM; i++) {
+		if (i % 10000 == 0)
+			printf("%i\n", i);
+
+		coprimes = 1;
+		for (j = 2; j<i; j++) {
+			if (is_coprime(i, j))
+				coprimes += 1;
+		}
+
+		if (((double)i / coprimes) > greatest) {
+			greatest = i;
+			ratio = (double)i / coprimes;
+		}
+	}
+
+	printf("number: %i\n", greatest);
+	printf("ratio : %f\n", ratio);
+	return 1;
+}
+
+
+