Data commit

Task/Mertens-function/C/mertens-function.c

@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int* mertens_numbers(int max) {
+    int* m = malloc((max + 1) * sizeof(int));
+    if (m == NULL)
+        return m;
+    m[1] = 1;
+    for (int n = 2; n <= max; ++n) {
+        m[n] = 1;
+        for (int k = 2; k <= n; ++k)
+            m[n] -= m[n/k];
+    }
+    return m;
+}
+
+int main() {
+    const int max = 1000;
+    int* mertens = mertens_numbers(max);
+    if (mertens == NULL) {
+        fprintf(stderr, "Out of memory\n");
+        return 1;
+    }
+    printf("First 199 Mertens numbers:\n");
+    const int count = 200;
+    for (int i = 0, column = 0; i < count; ++i) {
+        if (column > 0)
+            printf(" ");
+        if (i == 0)
+            printf("  ");
+        else
+            printf("%2d", mertens[i]);
+        ++column;
+        if (column == 20) {
+            printf("\n");
+            column = 0;
+        }
+    }
+    int zero = 0, cross = 0, previous = 0;
+    for (int i = 1; i <= max; ++i) {
+        int m = mertens[i];
+        if (m == 0) {
+            ++zero;
+            if (previous != 0)
+                ++cross;
+        }
+        previous = m;
+    }
+    free(mertens);
+    printf("M(n) is zero %d times for 1 <= n <= %d.\n", zero, max);
+    printf("M(n) crosses zero %d times for 1 <= n <= %d.\n", cross, max);
+    return 0;
+}