Data commit

Task/Hofstadter-Figure-Figure-sequences/C/hofstadter-figure-figure-sequences.c

@@ -0,0 +1,84 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+// simple extensible array stuff
+typedef unsigned long long xint;
+
+typedef struct {
+	size_t len, alloc;
+	xint *buf;
+} xarray;
+
+xarray rs, ss;
+
+void setsize(xarray *a, size_t size)
+{
+	size_t n = a->alloc;
+	if (!n) n = 1;
+
+	while (n < size) n <<= 1;
+	if (a->alloc < n) {
+		a->buf = realloc(a->buf, sizeof(xint) * n);
+		if (!a->buf) abort();
+		a->alloc = n;
+	}
+}
+
+void push(xarray *a, xint v)
+{
+	while (a->alloc <= a->len)
+		setsize(a, a->alloc * 2);
+
+	a->buf[a->len++] = v;
+}
+
+
+// sequence stuff
+void RS_append(void);
+
+xint R(int n)
+{
+	while (n > rs.len) RS_append();
+	return rs.buf[n - 1];
+}
+
+xint S(int n)
+{
+	while (n > ss.len) RS_append();
+	return ss.buf[n - 1];
+}
+
+void RS_append()
+{
+	int n = rs.len;
+	xint r = R(n) + S(n);
+	xint s = S(ss.len);
+
+	push(&rs, r);
+	while (++s < r) push(&ss, s);
+	push(&ss, r + 1); // pesky 3
+}
+
+int main(void)
+{
+	push(&rs, 1);
+	push(&ss, 2);
+
+	int i;
+	printf("R(1 .. 10):");
+	for (i = 1; i <= 10; i++)
+		printf(" %llu", R(i));
+
+	char seen[1001] = { 0 };
+	for (i = 1; i <=  40; i++) seen[ R(i) ] = 1;
+	for (i = 1; i <= 960; i++) seen[ S(i) ] = 1;
+	for (i = 1; i <= 1000 && seen[i]; i++);
+
+	if (i <= 1000) {
+		fprintf(stderr, "%d not seen\n", i);
+		abort();
+	}
+
+	puts("\nfirst 1000 ok");
+	return 0;
+}