tasks a-s

Task/Self-referential-sequence/C/self-referential-sequence.c

@@ -0,0 +1,123 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct rec_t rec_t;
+struct rec_t {
+	int depth;
+	rec_t * p[10];
+};
+
+rec_t root = {0, {0}};
+
+#define USE_POOL_ALLOC
+#ifdef USE_POOL_ALLOC /* not all that big a deal */
+rec_t *tail = 0, *head = 0;
+#define POOL_SIZE (1 << 20)
+inline rec_t *new_rec()
+{
+	if (head == tail) {
+		head = calloc(sizeof(rec_t), POOL_SIZE);
+		tail = head + POOL_SIZE;
+	}
+	return head++;
+}
+#else
+#define new_rec() calloc(sizeof(rec_t), 1)
+#endif
+
+rec_t *find_rec(char *s)
+{
+	int i;
+	rec_t *r = &root;
+	while (*s) {
+		i = *s++ - '0';
+		if (!r->p[i]) r->p[i] = new_rec();
+		r = r->p[i];
+	}
+	return r;
+}
+
+/* speed up number to string conversion */
+char number[100][4];
+void init()
+{
+	int i;
+	for (i = 0; i < 100; i++)
+		sprintf(number[i], "%d", i);
+}
+
+void count(char *buf)
+{
+	int i, c[10] = {0};
+	char *s;
+
+	for (s = buf; *s; c[*s++ - '0']++);
+
+	for (i = 9; i >= 0; i--) {
+		if (!c[i]) continue;
+		s = number[c[i]];
+
+		*buf++ = s[0];
+		if ((*buf = s[1])) buf++;
+
+		*buf++ = i + '0';
+	}
+
+	*buf = '\0';
+}
+
+int depth(char *in, int d)
+{
+	rec_t *r = find_rec(in);
+
+	if (r->depth > 0)
+		return r->depth;
+
+	d++;
+	if (!r->depth)	r->depth = -d;
+	else		r->depth += d;
+
+	count(in);
+	d = depth(in, d);
+
+	if (r->depth <= 0) r->depth = d + 1;
+	return r->depth;
+}
+
+int main(void)
+{
+	char a[100];
+	int i, d, best_len = 0, n_best = 0;
+	int best_ints[32];
+	rec_t *r;
+
+	init();
+
+	for (i = 0; i < 1000000; i++) {
+		sprintf(a, "%d", i);
+		d = depth(a, 0);
+
+		if (d < best_len) continue;
+		if (d > best_len) {
+			n_best = 0;
+			best_len = d;
+		}
+		if (d == best_len)
+			best_ints[n_best++] = i;
+	}
+
+	printf("longest length: %d\n", best_len);
+	for (i = 0; i < n_best; i++) {
+		printf("%d\n", best_ints[i]);
+		sprintf(a, "%d", best_ints[i]);
+		for (d = 0; d <= best_len; d++) {
+			r = find_rec(a);
+			printf("%3d: %s\n", r->depth, a);
+			count(a);
+		}
+		putchar('\n');
+	}
+
+	return 0;
+}