solve day 8

day7.c

@@ -1,5 +1,4 @@
 #include <limits.h>
-#include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/param.h>

day8.c

@@ -0,0 +1,119 @@
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/param.h>
+
+#include "aoc.h"
+
+typedef struct {
+	uint8_t **data;
+	size_t width, height;
+} day8_Map;
+
+static void *day8_parse(char **lines, int line_count)
+{
+	day8_Map *map = malloc(sizeof(day8_Map));
+	map->height = line_count;
+	map->width = strlen(lines[0]);
+	map->data = malloc(map->height*sizeof(uint8_t*));
+	for (int y = 0; y < map->height; y++) {
+		map->data[y] = malloc(map->width*sizeof(uint8_t));
+		for (int x = 0; x < map->width; x++) {
+			map->data[y][x] = lines[y][x] - '0';
+		}
+	}
+	return map;
+}
+
+static bool is_visible_horizontal(day8_Map *map, uint8_t value, int x0, int x1, int y)
+{
+	for (int xi = x0; xi < x1; xi++) {
+		if (map->data[y][xi] >= value) return false;
+	}
+	return true;
+}
+
+static bool is_visible_vertical(day8_Map *map, uint8_t value, int x, int y0, int y1)
+{
+	for (int yi = y0; yi < y1; yi++) {
+		if (map->data[yi][x] >= value) return false;
+	}
+	return true;
+}
+
+static bool is_visible(day8_Map *map, int x, int y) {
+	uint8_t current = map->data[y][x];
+	return is_visible_horizontal (map, current, x+1, map->width, y) ||
+					is_visible_horizontal(map, current, 0, x, y) ||
+					is_visible_vertical  (map, current, x, y+1, map->height) ||
+					is_visible_vertical  (map, current, x, 0, y);
+}
+
+static int get_horizontal_edge(day8_Map *map, uint8_t value, int x0, int x1, int y)
+{
+	if (x0 <= x1) {
+		for (int xi = x0; xi <= x1; xi++) {
+			if (map->data[y][xi] >= value) return xi;
+		}
+	} else {
+		for (int xi = x0; xi >= x1; xi--) {
+			if (map->data[y][xi] >= value) return xi;
+		}
+	}
+	return x1;
+}
+
+static int get_vertical_edge(day8_Map *map, uint8_t value, int x, int y0, int y1)
+{
+	if (y0 <= y1) {
+		for (int yi = y0; yi <= y1; yi++) {
+			if (map->data[yi][x] >= value) return yi;
+		}
+	} else {
+		for (int yi = y0; yi >= y1; yi--) {
+			if (map->data[yi][x] >= value) return yi;
+		}
+	}
+	return y1;
+}
+
+static int get_score(day8_Map *map, int x, int y) {
+	uint8_t value = map->data[y][x];
+	int right_edge  = get_horizontal_edge(map, value, x+1, map->width-1, y);
+	int left_edge   = get_horizontal_edge(map, value, x-1, 0  , y);
+	int bottom_edge = get_vertical_edge  (map, value, x, y+1, map->height-1);
+	int top_edge    = get_vertical_edge  (map, value, x, y-1, 0);
+	return (right_edge - x) * (x - left_edge) * (bottom_edge - y) * (y - top_edge);
+}
+
+static void day8_part1(void *p)
+{
+	day8_Map *map = p;
+
+	int result = map->height * map->width - (map->height-2) * (map->width-2);
+	for (int y = 1; y < map->height-1; y++) {
+		for (int x = 1; x < map->width-1; x++) {
+			result += is_visible(map, x, y);
+		}
+	}
+
+	printf("%d\n", result);
+}
+
+static void day8_part2(void *p)
+{
+	day8_Map *map = p;
+
+	int result = 0;
+	for (int y = 1; y < map->height-1; y++) {
+		for (int x = 1; x < map->width-1; x++) {
+			result = MAX(result, get_score(map, x, y));
+		}
+	}
+
+	printf("%d\n", result);
+}
+
+ADD_SOLUTION(8, day8_parse, day8_part1, day8_part2);

main.c

@@ -15,6 +15,7 @@
 #include "day5.c"
 #include "day6.c"
 #include "day7.c"
+#include "day8.c"
 
 Solution *find_solution(int day)
 {