advent2021

commit 6aef118d598a26b339a578dd83e6dbb09366bacd
parent 99aed221f29a7174d0cddebc9003dbc6779b3d0d
Author: bsandro <[email protected]>
Date:   Sun,  5 Dec 2021 16:12:14 +0200

Day 05, puzzle 2

Diffstat:
M
day05/puzzle.c
 | 
105
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------------------

1 file changed, 77 insertions(+), 28 deletions(-)
diff --git a/day05/puzzle.c b/day05/puzzle.c
@@ -15,7 +15,8 @@
 #define MAP_SIZE 1000
 
 // being tad lazy here - assume that the map sides are no larger than MAP_SIZE
-static short map[MAP_SIZE][MAP_SIZE];
+static short map1[MAP_SIZE][MAP_SIZE];
+static short map2[MAP_SIZE][MAP_SIZE];
 
 struct vec2_t {
 	int x;
@@ -32,8 +33,10 @@ struct vec2_pair_t make_pair(const char *str);
 struct vec2_t make_vec2(const char *str);
 void swap_vec2(struct vec2_t *a, struct vec2_t *b); // swap a and b
 void print_pair(const struct vec2_pair_t *pair);
+bool is_pair_diagonal(const struct vec2_pair_t *pair);
 void normalize_pair(struct vec2_pair_t *pair); // ensure begin is always smaller number
-int mark_map(const struct vec2_pair_t *pair);
+int mark_map1(const struct vec2_pair_t *pair);
+int mark_map2(const struct vec2_pair_t *pair);
 void print_map();
 
 /* ****************************************************************** */
@@ -47,15 +50,17 @@ void puzzle(const char *filename, int *result1, int *result2) {
 
 	char buf[STR_LEN] = {0};
 	unsigned int line_num = 0;
-	int danger_points = 0;
+
+	*result1 = 0;
+	*result2 = 0;
 
 	while (fgets(buf, STR_LEN, infile) != NULL) {
 		struct vec2_pair_t pair = make_pair(buf);
-		// only straight lines
-		if (pair.a.x == pair.b.x || pair.a.y == pair.b.y) {
+		// only straight and 45deg diagonal lines
+		if (pair.a.x == pair.b.x || pair.a.y == pair.b.y || is_pair_diagonal(&pair)) {
 			normalize_pair(&pair);
-			//print_pair(&pair);
-			danger_points += mark_map(&pair);
+			*result1 += mark_map1(&pair);
+			*result2 += mark_map2(&pair);
 		}
 
 		++line_num;
@@ -64,9 +69,6 @@ void puzzle(const char *filename, int *result1, int *result2) {
 
 	//print_map();
 
-	*result1 = danger_points;
-	*result2 = 0;
-
 	// mutiny! ignoring feof/ferror.
 	fclose(infile);
 }
@@ -125,10 +127,10 @@ void print_map() {
 	printf("\n--------MAP-----------\n");
 	for (int y = 0; y < MAP_SIZE; ++y) {
 		for (int x = 0; x < MAP_SIZE; ++x) {
-			if (map[x][y] == 0) {
+			if (map2[x][y] == 0) {
 				printf(".");
 			} else {
-				printf("%d", map[x][y]);
+				printf("%d", map2[x][y]);
 			}
 		}
 		printf("\n");
@@ -136,36 +138,83 @@ void print_map() {
 	printf("\n-----------------------\n");
 }
 
+bool is_pair_diagonal(const struct vec2_pair_t *pair) {
+	return abs(pair->a.x - pair->b.x) == abs(pair->a.y - pair->b.y);
+}
+
 void normalize_pair(struct vec2_pair_t *pair) {
-	if (pair->a.x == pair->b.x) {
-		if (pair->a.y > pair->b.y) {
-			swap_vec2(&pair->a, &pair->b);
+	if (pair->a.x == pair->b.x && pair->a.y > pair->b.y) {
+		// straight verticals
+		swap_vec2(&pair->a, &pair->b);
+	} else if (pair->a.y == pair->b.y && pair->a.x > pair->b.x) {
+		// straight horizontals
+		swap_vec2(&pair->a, &pair->b);
+	} else if (is_pair_diagonal(pair) && pair->a.x > pair->b.x) {
+		// normalize diagonals only by x axis
+		swap_vec2(&pair->a, &pair->b);
+	}
+}
+
+int mark_map1(const struct vec2_pair_t *pair) {
+	int count = 0;
+
+	if (pair->a.x == pair->b.x) { // vertical lines
+		int x = pair->a.x;
+		for (int y = pair->a.y; y <= pair->b.y; ++y) {
+			if (++map1[x][y] == 2) {
+				++count;
+			}
 		}
-	} else if (pair->a.y == pair->b.y) {
-		if (pair->a.x > pair->b.x) {
-			swap_vec2(&pair->a, &pair->b);
+	} else if (pair->a.y == pair->b.y) { // horizontal lines
+		int y = pair->a.y;
+		for (int x = pair->a.x; x <= pair->b.x; ++x) {
+			if (++map1[x][y] == 2) {
+				++count;
+			}
 		}
 	}
+
+	return count;
 }
 
-int mark_map(const struct vec2_pair_t *pair) {
-	int sum = 0;
-	// @todo tidy up?
-	if (pair->a.x == pair->b.x) {
+int mark_map2(const struct vec2_pair_t *pair) {
+	int count = 0;
+
+	if (pair->a.x == pair->b.x) { // vertical lines
 		int x = pair->a.x;
 		for (int y = pair->a.y; y <= pair->b.y; ++y) {
-			if (++map[x][y] == 2) { // only counting each overlap once
-				++sum;
+			if (++map2[x][y] == 2) {
+				++count;
 			}
 		}
-	} else if (pair->a.y == pair->b.y) {
+	} else if (pair->a.y == pair->b.y) { // horizontal lines
 		int y = pair->a.y;
 		for (int x = pair->a.x; x <= pair->b.x; ++x) {
-			if (++map[x][y] == 2) {
-				++sum;
+			if (++map2[x][y] == 2) {
+				++count;
+			}
+		}
+	} else if (is_pair_diagonal(pair)) { // diagonal lines
+		int x = pair->a.x;
+		int y = pair->a.y;
+		if (pair->a.y < pair->b.y) {
+			for (; x <= pair->b.x && y <= pair->b.y;) {
+				if (++map2[x][y] == 2) {
+					++count;
+				}
+				++x;
+				++y;
+			}
+		} else {
+			for (; x <= pair->b.x && y >= pair->b.y;) {
+				if (++map2[x][y] == 2) {
+					++count;
+				}
+				++x;
+				--y;
 			}
 		}
 	}
 
-	return sum;
+	return count;
 }