solve day 9

Makefile

@@ -1,4 +1,4 @@
-main: main.c day*.c vec.h aoc.h
+main: main.c day*.c vec.h aoc.h point.h
 	gcc -o main main.c -lcurl
 
 run: main

day9.c

@@ -0,0 +1,213 @@
+#include <stdio.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <sys/param.h>
+
+#include "aoc.h"
+#include "point.h"
+
+typedef enum {
+	MOVE_DIR_UP,
+	MOVE_DIR_DOWN,
+	MOVE_DIR_LEFT,
+	MOVE_DIR_RIGHT,
+} MOVE_DIR;
+
+typedef struct {
+	MOVE_DIR dir;
+	int count;
+} RopeMove;
+
+typedef struct {
+	RopeMove *moves;
+	int count;
+} day9_Data;
+
+static MOVE_DIR parse_move_dir(char dir)
+{
+	switch (dir) {
+		case 'R': return MOVE_DIR_RIGHT;
+		case 'L': return MOVE_DIR_LEFT;
+		case 'U': return MOVE_DIR_UP;
+		case 'D': return MOVE_DIR_DOWN;
+	}
+	abort();
+}
+
+static void *day9_parse(char **lines, int line_count)
+{
+	day9_Data *data = malloc(sizeof(day9_Data));
+	data->moves = malloc(line_count * sizeof(RopeMove));
+	data->count = line_count;
+
+	for (int i = 0; i < line_count; i++) {
+		char *line = lines[i];
+		RopeMove *move = &data->moves[i];
+		move->dir = parse_move_dir(line[0]);
+		move->count = atoi(line+2);
+	}
+
+	return data;
+}
+
+static int sign(int x)
+{
+	return x > 0 ? 1 : -1;
+}
+
+static void get_bounding_box(day9_Data *moves, int *ox, int *oy, int *width, int *height)
+{
+	int minx = 0, maxx = 0;
+	int miny = 0, maxy = 0;
+	int x = 0, y = 0;
+	for (int i = 0; i < moves->count; i++) {
+		RopeMove *move = &moves->moves[i];
+		switch (move->dir) {
+			case MOVE_DIR_UP:
+				y -= move->count;
+				break;
+			case MOVE_DIR_DOWN:
+				y += move->count;
+				break;
+			case MOVE_DIR_LEFT:
+				x -= move->count;
+				break;
+			case MOVE_DIR_RIGHT:
+				x += move->count;
+				break;
+		}
+		minx = MIN(x, minx);
+		maxx = MAX(x, maxx);
+		miny = MIN(y, miny);
+		maxy = MAX(y, maxy);
+	}
+
+	*ox = -minx;
+	*oy = -miny;
+	*width = maxx - minx + 1;
+	*height = maxy - miny + 1;
+}
+
+static void get_move_direction(MOVE_DIR dir, int *dx, int *dy)
+{
+	switch (dir) {
+		case MOVE_DIR_UP:
+			*dy = -1;
+			break;
+		case MOVE_DIR_DOWN:
+			*dy = 1;
+			break;
+		case MOVE_DIR_LEFT:
+			*dx = -1;
+			break;
+		case MOVE_DIR_RIGHT:
+			*dx = 1;
+			break;
+	}
+}
+
+static void follow_point(Point *tail, Point *head)
+{
+	int diffx = abs(head->x - tail->x);
+	int diffy = abs(head->y - tail->y);
+	if (diffx > 1 || diffy > 1) {
+		if (diffx + diffy > 2) {
+			tail->x += sign(head->x - tail->x);
+			tail->y += sign(head->y - tail->y);
+		} else if (diffx > 1) {
+			tail->x += sign(head->x - tail->x);
+		} else if (diffy > 1) {
+			tail->y += sign(head->y - tail->y);
+		}
+	}
+}
+
+static void day9_part1(void *p)
+{
+	day9_Data *moves = p;
+
+	int ox, oy, width, height;
+	get_bounding_box(moves, &ox, &oy, &width, &height);
+
+	bool map[width][height];
+	for (int y = 0; y < height; y++) {
+		for (int x = 0; x < width; x++) {
+			map[x][y] = false;
+		}
+	}
+	map[ox][oy] = true;
+
+	Point head = { 0, 0 };
+	Point tail = { 0, 0 };
+	for (int i = 0; i < moves->count; i++) {
+		RopeMove *move = &moves->moves[i];
+		int dx = 0, dy = 0;
+		get_move_direction(move->dir, &dx, &dy);
+		for (int j = 0; j < move->count; j++) {
+			head.x += dx;
+			head.y += dy;
+
+			follow_point(&tail, &head);
+			map[tail.x+ox][tail.y+oy] = true;
+		}
+	}
+
+	int result = 0;
+	for (int y = 0; y < height; y++) {
+		for (int x = 0; x < width; x++) {
+			result += map[x][y];
+		}
+	}
+	printf("%d\n", result);
+}
+
+static void day9_part2(void *p)
+{
+	day9_Data *moves = p;
+
+	int ox, oy, width, height;
+	get_bounding_box(moves, &ox, &oy, &width, &height);
+
+	bool map[width][height];
+	for (int y = 0; y < height; y++) {
+		for (int x = 0; x < width; x++) {
+			map[x][y] = false;
+		}
+	}
+	map[ox][oy] = true;
+
+	int rope_size = 10;
+	Point rope[rope_size];
+	for (int i = 0; i < rope_size; i++) {
+		rope[i].x = 0;
+		rope[i].y = 0;
+	}
+
+	for (int i = 0; i < moves->count; i++) {
+		RopeMove *move = &moves->moves[i];
+		int dx = 0, dy = 0;
+		get_move_direction(move->dir, &dx, &dy);
+		for (int _ = 0; _ < move->count; _++) {
+			Point *head = &rope[0];
+			head->x += dx;
+			head->y += dy;
+
+			for (int j = 1; j < rope_size; j++) {
+				follow_point(&rope[j], &rope[j-1]);
+			}
+
+			Point *tail = &rope[rope_size-1];
+			map[tail->x+ox][tail->y+oy] = true;
+		}
+	}
+
+	int result = 0;
+	for (int y = 0; y < height; y++) {
+		for (int x = 0; x < width; x++) {
+			result += map[x][y];
+		}
+	}
+	printf("%d\n", result);
+}
+
+ADD_SOLUTION(9, day9_parse, day9_part1, day9_part2);

main.c

@@ -16,6 +16,7 @@
 #include "day6.c"
 #include "day7.c"
 #include "day8.c"
+#include "day9.c"
 
 Solution *find_solution(int day)
 {

point.h

@@ -0,0 +1,8 @@
+#ifndef POINT_H_
+#define POINT_H_
+
+typedef struct {
+	int x, y;
+} Point;
+
+#endif //POINT_H_