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Task/Digital-root-Multiplicative-digital-root/C/digital-root-multiplicative-digital-root.c

@@ -0,0 +1,58 @@
+#include <stdio.h>
+
+#define twidth 5
+#define mdr(rmdr, rmp, n)\
+    do { *rmp = 0; _mdr(rmdr, rmp, n); } while (0)
+
+void _mdr(int *rmdr, int *rmp, long long n)
+{
+    /* Adjust r if 0 case, so we don't return 1 */
+    int r = n ? 1 : 0;
+    while (n) {
+        r *= (n % 10);
+        n /= 10;
+    }
+
+    (*rmp)++;
+    if (r >= 10)
+        _mdr(rmdr, rmp, r);
+    else
+        *rmdr = r;
+}
+
+int main(void)
+{
+    int i, j, vmdr, vmp;
+    const int values[] = { 123321, 7739, 893, 899998 };
+    const int vsize    = sizeof(values) / sizeof(values[0]);
+
+    /* Initial test values */
+    printf("Number    MDR    MP\n");
+    for (i = 0; i < vsize; ++i) {
+        mdr(&vmdr, &vmp, values[i]);
+        printf("%6d   %3d   %3d\n", values[i], vmdr, vmp);
+    }
+
+    /* Determine table values */
+    int table[10][twidth] = { 0 };
+    int tfill[10]         = { 0 };
+    int total             = 0;
+    for (i = 0; total < 10 * twidth; ++i) {
+        mdr(&vmdr, &vmp, i);
+        if (tfill[vmdr] < twidth) {
+            table[vmdr][tfill[vmdr]++] = i;
+            total++;
+        }
+    }
+
+    /* Print calculated table values */
+    printf("\nMDR: [n0..n4]\n");
+    for (i = 0; i < 10; ++i) {
+        printf("%3d: [", i);
+        for (j = 0; j < twidth; ++j)
+            printf("%d%s", table[i][j], j != twidth - 1 ? ", " : "");
+        printf("]\n");
+    }
+
+    return 0;
+}