Solve day 3 part 1

1 files changed, 76 insertions, 0 deletions

diff --git a/2019/day03.c b/2019/day03.c
new file mode 100644
index 0000000..5d45bc0
--- /dev/null
+++ b/2019/day03.c
@@ -0,0 +1,76 @@
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+struct Point {
+	int x, y;
+};
+
+struct Line {
+	struct Point a, b;
+};
+
+static void normalize(struct Line *l) {
+	if (l->a.x > l->b.x || l->a.y > l->b.y) {
+		struct Point p = l->a;
+		l->a = l->b;
+		l->b = p;
+	}
+}
+
+static size_t parse(struct Line *lines) {
+	char dir;
+	int dist;
+	size_t len = 0;
+	struct Point point = { 0, 0 };
+	while (EOF != scanf("%c%d,", &dir, &dist)) {
+		if (dir == '\n') break;
+		lines[len].a = point;
+		switch (dir) {
+			break; case 'U': point.y += dist;
+			break; case 'D': point.y -= dist;
+			break; case 'L': point.x -= dist;
+			break; case 'R': point.x += dist;
+			break; default: abort();
+		}
+		lines[len].b = point;
+		normalize(&lines[len++]);
+	}
+	return len;
+}
+
+static int intersect(struct Point *p, struct Line v, struct Line h) {
+	if (v.a.x != v.b.x) {
+		struct Line l = v;
+		v = h;
+		h = l;
+	}
+	if (v.a.y == v.b.y) return 0;
+	if (h.a.x == h.b.x) return 0;
+	if (h.a.y < v.a.y) return 0;
+	if (h.a.y > v.b.y) return 0;
+	if (h.a.x > v.a.x) return 0;
+	if (h.b.x < v.a.x) return 0;
+	p->x = v.a.x;
+	p->y = h.a.y;
+	return 1;
+}
+
+int main(void) {
+	struct Line aLines[512];
+	struct Line bLines[512];
+	size_t aLen = parse(aLines);
+	size_t bLen = parse(bLines);
+
+	int min = INT_MAX;
+	for (size_t a = 0; a < aLen; ++a) {
+		for (size_t b = 0; b < bLen; ++b) {
+			struct Point p;
+			if (!intersect(&p, aLines[a], bLines[b])) continue;
+			if (!p.x && !p.y) continue;
+			int dist = abs(p.x) + abs(p.y);
+			if (dist < min) min = dist;
+		}
+	}
+	printf("%d\n", min);
+}