Solve puzzle 9 part 2

Needed to switch to moving the head one step at a time and recalcating
the rest of the rope on each iteration, or the numbers came out wrong.

1 files changed, 93 insertions, 43 deletions

diff --git a/9.c b/9.c
index 344c137..e8418bf 100644
--- a/9.c
+++ b/9.c
@@ -5,6 +5,7 @@
 #include <search.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 
 struct point {
@@ -14,17 +15,24 @@ struct point {
 
 
 struct point *
-point_copy(struct point const * other)
+point_create(int x, int y)
 {
 	struct point * p = malloc(sizeof(struct point));
 	if (!p)
 		return NULL;
-	p->x = other->x;
-	p->y = other->y;
+	p->x = x;
+	p->y = y;
 	return p;
 }
 
 
+struct point *
+point_copy(struct point const * other)
+{
+	return point_create(other->x, other->y);
+}
+
+
 int
 point_cmp(struct point const * a, struct point const * b)
 {
@@ -42,19 +50,49 @@ point_tcmp(void const * a, void const * b)
 
 
 int
-main()
+main(int argc, char ** argv)
 {
+	int len = 2, i;
 	char buf[BUFSIZ];
-	struct point head = {0}, * tail = point_copy(&head);
+	struct point * rope;
 	void * tails = NULL;
 	int ntails = 0;
 
-	tsearch(tail, &tails, point_tcmp);
-	tail = point_copy(tail);
+	while ((i = getopt(argc, argv, "p:l:")) != -1) {
+		switch (i) {
+		case 'p':
+			switch (atoi(optarg)) {
+			case 1: len = 2; break;
+			case 2: len = 10; break;
+			default:
+				fprintf(stderr, "Unexpected part: %s\n", optarg);
+				return -1;
+			}
+			break;
+
+		case 'l':
+			len = atoi(optarg);
+			if (len < 2) {
+				fprintf(stderr, "Unexpected length: %d\n", len);
+				return -1;
+			}
+			break;
+
+		default:
+			return -1;
+		}
+	}
+
+	rope = malloc(len * sizeof(struct point));
+	for (i = 0; i < len; ++i) {
+		rope[i].x = rope[i].y = 0;
+	}
+
+	tsearch(point_create(0, 0), &tails, point_tcmp);
 	++ntails;
 
 	while (fgets(buf, sizeof(buf), stdin)) {
-		int dist, dx, dy;
+		int dist;
 
 		if (!isalpha(buf[0])
 				|| buf[1] != ' '
@@ -69,51 +107,63 @@ main()
 			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;
-		}
+		while (dist > 0) {
+			int seg;
+
+			switch (buf[0]) {
+				case 'L': --rope[0].x; break;
+				case 'R': ++rope[0].x; break;
+				case 'U': ++rope[0].y; break;
+				case 'D': --rope[0].y; break;
+				default:
+					  fprintf(stderr, "Unexpected input: %s\n", buf);
+					  return -1;
+			}
 
-		dx = head.x - tail->x;
-		dy = head.y - tail->y;
-		while (dx * dx + dy * dy > 2) {
-			struct point ** pp;
+			for (seg = 1; seg < len; ++seg) {
+				int dx, dy;
 
-			if (dx > 0) {
-				++tail->x;
-				--dx;
-			}
-			if (dx < 0) {
-				--tail->x;
-				++dx;
-			}
-			if (dy > 0) {
-				++tail->y;
-				--dy;
-			}
-			if (dy < 0) {
-				--tail->y;
-				++dy;
+				dx = rope[seg - 1].x - rope[seg].x;
+				dy = rope[seg - 1].y - rope[seg].y;
+
+				if (dx * dx + dy * dy <= 2)
+					break;
+
+				if (dx > 0)
+					++rope[seg].x;
+				if (dx < 0)
+					--rope[seg].x;
+				if (dy > 0)
+					++rope[seg].y;
+				if (dy < 0)
+					--rope[seg].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
-				tail = point_copy(tail);
-				++ntails;
+			if (seg == len) {
+				// Had to move all segments, including tail.
+				// Check if it's a new tail pos
+				struct point * tail, ** pp;
+
+				// Search/insert current tail in visited tails
+				tail = point_copy(rope + len - 1);
+				pp = tsearch(tail, &tails, point_tcmp);
+				if (*pp == tail) {
+					// This was a new one, tail is now in the tree
+					++ntails;
+				}
+				else {
+					// Tail already in tree, free the one we just created.
+					free(tail);
+				}
 			}
+
+			--dist;
 		}
 	}
 
 	printf("Unique tail spots visited: %d\n", ntails);
 
-	free(tail);
+	free(rope);
 #ifdef _GNU_SOURCE
 	tdestroy(tails, free);
 #endif