advent2023

commit 18d1e368688d5515276ce16a2e526d73563116c0
parent 1094963efd3db16c43de4349b1ef3c1514e60f64
Author: bsandro <email@bsandro.tech>
Date:   Sun,  3 Dec 2023 17:53:32 +0200

day 03 p2 aka "nothing beats good old linked lists"

Diffstat:
M
.gitignore
 | 
1
+
M
day03/puzzle.c
 | 
70
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---

2 files changed, 68 insertions(+), 3 deletions(-)
diff --git a/.gitignore b/.gitignore
@@ -1 +1,2 @@
 *.o
+*.swp
diff --git a/day03/puzzle.c b/day03/puzzle.c
@@ -11,13 +11,39 @@
 
 #define STR_LEN 2048
 // 140x140 for real one
-#define FIELD_SIZE 10
-//#define FIELD_SIZE 140
+//#define FIELD_SIZE 10
+#define FIELD_SIZE 140
 
 bool is_digit(char b) {
 	return b>='0' && b<='9';
 }
 
+typedef struct Gear {
+	int pos; // y * FIELD_SIZE + x
+	int part;
+	struct Gear *next;
+} Gear;
+
+Gear * find_gear(Gear *gears, int pos) {
+	Gear *gear = gears;
+	while (gear != NULL) {
+		if (gear->pos == pos) {
+			return gear;
+		}
+		gear = gear->next;
+	}
+	return NULL;
+}
+
+Gear * make_gear(Gear *prev) {
+	Gear *gear = malloc(sizeof(Gear));
+	memset(gear, 0, sizeof(Gear));
+	if (prev!=NULL) {
+		prev->next = gear;
+	}
+	return gear;
+}
+
 bool check_part(int x, int y, const char (*field)[FIELD_SIZE][FIELD_SIZE]) {
 	for (int dy=-1; dy<=1; ++dy) {
 		for (int dx=-1; dx<=1; ++dx) {
@@ -33,6 +59,21 @@ bool check_part(int x, int y, const char (*field)[FIELD_SIZE][FIELD_SIZE]) {
 	return false;
 }
 
+int check_gear(int x, int y, const char (*field)[FIELD_SIZE][FIELD_SIZE]) {
+	for (int dy=-1; dy<=1; ++dy) {
+		for (int dx=-1; dx<=1; ++dx) {
+			int dy1=y+dy;
+			int dx1=x+dx;
+			if (dy1>=0 && dy1<FIELD_SIZE && dx1>=0 && dx1<FIELD_SIZE) {
+				if ((*field)[dy1][dx1]=='*') {
+					return dy1*FIELD_SIZE+dx1;
+				}
+			}
+		}
+	}
+	return -1;
+}
+
 void puzzle(const char *filename, long long *result1, long long *result2) {
 	FILE *infile = fopen(filename, "r");
 	if (infile == NULL) {
@@ -58,20 +99,43 @@ void puzzle(const char *filename, long long *result1, long long *result2) {
 	// mutiny! ignoring feof/ferror.
 	fclose(infile);
 
+	Gear *gears = NULL;
+	Gear *gear_last = NULL;
+
 	for (int y=0; y<FIELD_SIZE; ++y) {
 		int x = 0;
 		while (x<FIELD_SIZE) {
 			int digit = 0;
 			bool is_part = false;
+			int gear_pos = -1;
 			while (is_digit(field[y][x++])) {
 				int cx = x-1;
 				if (cx>=FIELD_SIZE) break; // too lazy to make it sane
-				if (!is_part) is_part = check_part(cx, y, &field);
+				if (check_part(cx, y, &field)) is_part = true;
 				digit = digit*10 + field[y][cx] - '0';
+				if (gear_pos==-1) gear_pos = check_gear(cx, y, &field);
 			}
 			if (digit>0 && is_part) {
 				//printf("%d\n", digit);
 				*result1 += digit;
+
+				if (gear_pos != -1) {
+					Gear *gear = find_gear(gears, gear_pos);
+					if (gear!=NULL) {
+						*result2 += digit * gear->part;
+						gear->part = digit;
+					} else {
+						gear = make_gear(gear_last);
+						gear->pos = gear_pos;
+						gear->part = digit;
+						if (gears==NULL) gears = gear;
+
+						if (gear_last!=NULL) {
+							gear_last->next = gear;
+						}
+						gear_last = gear;
+					}
+				}
 			}
 		}
 	}