tasks a-s

Task/Self-describing-numbers/C/self-describing-numbers-1.c

@@ -0,0 +1,45 @@
+#include <stdio.h>
+
+int self_desc(const char *s)
+{
+	unsigned char cnt[10] = {0};
+	int i;
+	for (i = 0; s[i] != '\0'; i++) cnt[s[i] - '0']++;
+	for (i = 0; s[i] != '\0'; i++) if (cnt[i] + '0' != s[i]) return 0;
+	return 1;
+}
+
+void gen(int n)
+{
+	char d[11];
+	int one, i;
+	/* one = 0 may be confusing.  'one' is the number of digit 1s */
+	for (one = 0; one <= 2 && one < n - 2; one++) {
+		for (i = 0; i <= n; d[i++] = 0);
+
+		if ((d[0] = n - 2 - one) != 2) {
+			d[2] = d[d[0] - 0] = 1;
+			d[1] = 2;
+		} else {
+			d[1] = one ? 1 : 0;
+			d[2] = 2;
+		}
+
+		for (i = 0; i < n; d[i++] += '0');
+		if (self_desc(d)) printf("%s\n", d);
+	}
+}
+
+int main()
+{
+	int i;
+	const char *nums[] = { "1210", "1337", "2020", "21200", "3211000", "42101000", 0};
+
+	for (i = 0; nums[i]; i++)
+		printf("%s is %sself describing\n", nums[i],
+			self_desc(nums[i]) ? "" : "not ");
+
+	printf("\nAll autobiograph numbers:\n");
+	for (i = 0; i < 11; i++) gen(i);
+	return 0;
+}

Task/Self-describing-numbers/C/self-describing-numbers-2.c

@@ -0,0 +1,15 @@
+1210 is self describing
+1337 is not self describing
+2020 is self describing
+21200 is self describing
+3211000 is self describing
+42101000 is self describing
+
+All autobiograph numbers:
+2020
+1210
+21200
+3211000
+42101000
+521001000
+6210001000

Task/Self-describing-numbers/C/self-describing-numbers-3.c

@@ -0,0 +1,26 @@
+#include <stdio.h>
+
+inline int self_desc(unsigned long long xx)
+{
+	register unsigned int d, x;
+	unsigned char cnt[10] = {0}, dig[10] = {0};
+
+	for (d = 0; xx > ~0U; xx /= 10)
+		cnt[ dig[d++] = xx % 10 ]++;
+
+	for (x = xx; x; x /= 10)
+		cnt[ dig[d++] = x % 10 ]++;
+
+	while(d-- && dig[x++] == cnt[d]);
+
+	return d == -1;
+}
+
+int main()
+{
+	int i;
+	for (i = 1; i < 100000000; i++) /* don't handle 0 */
+		if (self_desc(i)) printf("%d\n", i);
+
+	return 0;
+}

Task/Self-describing-numbers/C/self-describing-numbers-4.c

@@ -0,0 +1,5 @@
+1210
+2020
+21200
+3211000
+42101000