From 0939249b408dce6ceab9c4637c2815b3b6f5f353 Mon Sep 17 00:00:00 2001
From: Adam Spragg <adam@spra.gg>
Date: Fri, 9 Dec 2022 13:18:34 +0000
Subject: First attempt at puzzle 9 part 1 (buggy)
Apparently the answer it gets for the full input (5736) is wrong. The
answer for the test input (13) is right though.
Added a bunch of debugging logic, to try and see *where* it's going
wrong, but I can't see it so far. This one is interesting.
---
9.c | 131 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
makefile | 1 +
2 files changed, 132 insertions(+)
create mode 100644 9.c
diff --git a/9.c b/9.c
new file mode 100644
index 0000000..d0c6a9f
--- /dev/null
+++ b/9.c
@@ -0,0 +1,131 @@
+
+//#define _GNU_SOURCE
+
+#include <ctype.h>
+#include <search.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+
+struct point {
+ int x;
+ int y;
+};
+
+
+struct point *
+point_copy(struct point const * other)
+{
+ struct point * p = malloc(sizeof(struct point));
+ if (!p)
+ return NULL;
+ p->x = other->x;
+ p->y = other->y;
+ return p;
+}
+
+
+int
+point_cmp(struct point const * a, struct point const * b)
+{
+ return a->x - b->x != 0
+ ? a->x - b->x
+ : a->y - b->y;
+}
+
+
+int
+point_tcmp(void const * a, void const * b)
+{
+ return point_cmp(a, b);
+}
+
+
+int
+main()
+{
+ char buf[BUFSIZ];
+ struct point head = {0}, * tail = point_copy(&head);
+ void * tails = NULL;
+ int ntails = 0;
+
+ tsearch(tail, &tails, point_tcmp);
+ ++ntails;
+ fprintf(stderr, "Tail visiting %d,%d\n", tail->x, tail->y);
+
+ while (fgets(buf, sizeof(buf), stdin)) {
+ int dist, dx, dy;
+
+ if (!isalpha(buf[0])
+ || buf[1] != ' '
+ || !isdigit(buf[2]))
+ {
+ fprintf(stderr, "Unexpected input: %s\n", buf);
+ return -1;
+ }
+
+ dist = atoi(buf + 2);
+ if (dist == 0) {
+ fprintf(stderr, "Unexpected distance in: %s\n", buf);
+ // Allow 0 for now...
+ }
+ switch (buf[0]) {
+ case 'L': head.x -= dist; break;
+ case 'R': head.x += dist; break;
+ case 'U': head.y += dist; break;
+ case 'D': head.y -= dist; break;
+ default:
+ fprintf(stderr, "Unexpected input: %s\n", buf);
+ return -1;
+ }
+ fprintf(stderr, "Head %c %d to %d,%d\n", buf[0], dist, head.x, head.y);
+
+ dx = head.x - tail->x;
+ dy = head.y - tail->y;
+ while (dx * dx + dy * dy > 2) {
+ struct point ** pp;
+
+ if (dx > 0) {
+ ++tail->x;
+ --dx;
+ }
+ if (dx < 0) {
+ --tail->x;
+ ++dx;
+ }
+ if (dy > 0) {
+ ++tail->y;
+ --dy;
+ }
+ if (dy < 0) {
+ --tail->y;
+ ++dy;
+ }
+ fprintf(stderr, " Tail visiting %d,%d", tail->x, tail->y);
+
+ // Search/insert current tail in visited tails
+ pp = tsearch(tail, &tails, point_tcmp);
+ if (*pp == tail) {
+ // This was a new one, tail is now in the tree
+ //fprintf(stderr, " (new)");
+ tail = point_copy(tail);
+ ++ntails;
+ }
+ else {
+ fprintf(stderr, " (old)");
+ }
+
+ fprintf(stderr, "\n");
+ }
+ }
+
+ printf("Unique tail spots visited: %d\n", ntails);
+
+ free(tail);
+#ifdef _GNU_SOURCE
+ tdestroy(tails, free);
+#endif
+
+ return 0;
+}
+
diff --git a/makefile b/makefile
index 6210dde..0268832 100644
--- a/makefile
+++ b/makefile
@@ -10,6 +10,7 @@ all: bin \
bin/6 \
bin/7 \
bin/8 \
+ bin/9 \
bin:
mkdir -p $@
--
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