From 861826d3ffcf75f67d8e207a8ec65ab0c6c4d80a Mon Sep 17 00:00:00 2001
From: Rokas Puzonas <rokas.puz@gmail.com>
Date: Sun, 11 Jun 2023 16:27:21 +0300
Subject: [PATCH] solve day 13

---
 aoc.h   |   1 +
 day12.c |   3 +-
 day13.c | 230 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 main.c  |   5 +-
 4 files changed, 236 insertions(+), 3 deletions(-)
 create mode 100644 day13.c

diff --git a/aoc.h b/aoc.h
index 4842da2..05c781e 100644
--- a/aoc.h
+++ b/aoc.h
@@ -2,6 +2,7 @@
 #define AOC_H_
 
 #include <stdbool.h>
+#include <stdlib.h>
 
 typedef void (*solution_cb)(void*);
 typedef void* (*parse_cb)(char** lines, int count);
diff --git a/day12.c b/day12.c
index dcf595d..743e9e7 100644
--- a/day12.c
+++ b/day12.c
@@ -1,12 +1,11 @@
 #include <assert.h>
 #include <stddef.h>
 #include <stdio.h>
-#include <stdlib.h>
 #include <string.h>
 
+#include "aoc.h"
 #include "types.h"
 #include "point.h"
-#include "aoc.h"
 
 typedef struct {
 	u8 *map;
diff --git a/day13.c b/day13.c
new file mode 100644
index 0000000..18acf16
--- /dev/null
+++ b/day13.c
@@ -0,0 +1,230 @@
+#include <assert.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/param.h>
+
+#include "types.h"
+#include "aoc.h"
+
+typedef struct day13_packet *day13_packet_ptr;
+
+struct day13_packet {
+	bool is_number;
+	union {
+		u8 number;
+		struct {
+			day13_packet_ptr list;
+			size_t list_size;
+		};
+	};
+};
+
+typedef struct {
+	struct day13_packet left;
+	struct day13_packet right;
+} day13_packet_pair;
+
+typedef struct {
+	day13_packet_pair* pairs;
+	size_t count;
+} day13_packet_pairs;
+
+static bool day13_is_digit(char c)
+{
+	return '0' <= c && c <= '9';
+}
+
+static size_t day13_parse_packet(struct day13_packet *result, char *packet)
+{
+	size_t bytes_read = 0;
+
+	if (packet[0] == '[') {
+		bytes_read++;
+		result->is_number = false;
+		result->list_size = 0;
+		result->list = NULL;
+		if (packet[1] != ']') {
+			while (true) {
+				result->list = realloc(result->list, sizeof(struct day13_packet)*(result->list_size+1));
+				bytes_read += day13_parse_packet(&result->list[result->list_size], packet+bytes_read);
+				result->list_size++;
+
+				if (packet[bytes_read] == ',') {
+					bytes_read++;
+					continue;
+				}
+				if (packet[bytes_read] == ']') break;
+				assert(false && "fuck");
+			}
+		}
+		bytes_read++;
+	} else if (day13_is_digit(packet[0])) {
+		bytes_read++;
+		result->is_number = true;
+		result->number = (packet[0] - '0');
+		for (int i = 1; i < strlen(packet); i++) {
+			if (!day13_is_digit(packet[i])) break;
+			result->number *= 10;
+			result->number += (packet[i] - '0');
+			bytes_read++;
+		}
+	} else {
+		assert(false && "Failed to parse packet");
+	}
+
+	return bytes_read;
+}
+
+static void printf_day13_packet(struct day13_packet *packet)
+{
+	if (packet->is_number) {
+		printf("%d", packet->number);
+	} else {
+		printf("[");
+		if (packet->list_size > 0) {
+			for (int i = 0; i < packet->list_size-1; i++) {
+				printf_day13_packet(&packet->list[i]);
+				printf(",");
+			}
+			printf_day13_packet(&packet->list[packet->list_size-1]);
+		}
+		printf("]");
+	}
+}
+
+static void *day13_parse(char **lines, int line_count)
+{
+	size_t n = (line_count+1)/3;
+	day13_packet_pair *pairs = malloc(sizeof(day13_packet_pair)*n);
+
+	for (int i = 0; i < n; i++)
+	{
+		day13_parse_packet(&pairs[i].left , lines[3*i+0]);
+		day13_parse_packet(&pairs[i].right, lines[3*i+1]);
+	}
+
+	day13_packet_pairs *result = malloc(sizeof(day13_packet_pairs));
+	result->pairs = pairs;
+	result->count = n;
+	return result;
+}
+
+// Return values:
+//  -1 = left is lower
+//   0 = equal
+//   1 = right is lower
+static int day13_compare(struct day13_packet *left, struct day13_packet *right)
+{
+	if (left->is_number && right->is_number) {
+		if (left->number == right->number) {
+			return 0;
+		} else if (left->number < right->number) {
+			return -1;
+		} else {
+			return 1;
+		}
+	} else if (!left->is_number && !right->is_number) {
+		for (int i = 0; i < MIN(left->list_size, right->list_size); i++) {
+			int item_result = day13_compare(&left->list[i], &right->list[i]);
+			if (item_result != 0) {
+				return item_result;
+			}
+		}
+		if (left->list_size < right->list_size) {
+			return -1;
+		} else if (left->list_size > right->list_size) {
+			return 1;
+		}
+	} else if (left->is_number && !right->is_number) {
+		struct day13_packet packet = {
+			.is_number = false,
+			.list = left,
+			.list_size = 1
+		};
+		return day13_compare(&packet, right);
+	} else if (!left->is_number && right->is_number) {
+		struct day13_packet packet = {
+			.is_number = false,
+			.list = right,
+			.list_size = 1
+		};
+		return day13_compare(left, &packet);
+	}
+	return 0;
+}
+
+static void day13_part1(void *p)
+{
+	day13_packet_pairs *pairs = (day13_packet_pairs*)p;
+	int result = 0;
+	for (int i = 0; i < pairs->count; i++) {
+		if (day13_compare(&pairs->pairs[i].left, &pairs->pairs[i].right) == -1) {
+			result += (i+1);
+		}
+	}
+	printf("Answer: %d\n", result);
+}
+
+static int day13_find_packet(struct day13_packet **packets, size_t count, struct day13_packet *target)
+{
+	for (int i = 0; i < count; i++) {
+		if (packets[i] == target) {
+			return i;
+		}
+	}
+	return -1;
+}
+
+static void day13_swap(struct day13_packet **A, struct day13_packet **B)
+{
+	struct day13_packet *C = *A;
+	*A = *B;
+	*B = C;
+}
+
+// bubble sort
+static void day13_sort_packets(struct day13_packet **packets, size_t count)
+{
+	for (int i = 0; i < count-1; i++) {
+		for (int j = i+1; j < count; j++) {
+			int cmp = day13_compare(packets[i], packets[j]);
+			if (cmp == 1) {
+				day13_swap(&packets[i], &packets[j]);
+			}
+		}
+	}
+}
+
+static void day13_part2(void *p)
+{
+	day13_packet_pairs *pairs = (day13_packet_pairs*)p;
+
+	size_t packet_count = pairs->count*2 + 2;
+	struct day13_packet **packets = malloc(sizeof(struct day13_packet*)*packet_count);
+
+	// insert divider [[2]]
+	struct day13_packet divider1;
+	day13_parse_packet(&divider1, "[[2]]");
+	packets[0] = &divider1;
+
+	// insert divider [[6]]
+	struct day13_packet divider2;
+	day13_parse_packet(&divider2, "[[6]]");
+	packets[1] = &divider2;
+
+	// insert packets from `pairs.pairs`
+	for (int i = 0; i < pairs->count; i++) {
+		packets[2 + i*2+0] = &pairs->pairs[i].left;
+		packets[2 + i*2+1] = &pairs->pairs[i].right;
+	}
+
+	day13_sort_packets(packets, packet_count);
+
+	int divider1_idx = day13_find_packet(packets, packet_count, &divider1);
+	int divider2_idx = day13_find_packet(packets, packet_count, &divider2);
+	int answer = (divider1_idx+1) * (divider2_idx+1);
+	printf("Answer: %d\n", answer);
+}
+
+ADD_SOLUTION(13, day13_parse, day13_part1, day13_part2);
diff --git a/main.c b/main.c
index d139258..a7f837e 100644
--- a/main.c
+++ b/main.c
@@ -21,6 +21,7 @@
 #include "day10.c"
 #include "day11.c"
 #include "day12.c"
+#include "day13.c"
 
 Solution *find_solution(int day)
 {
@@ -170,10 +171,12 @@ int main(int argc, char** argv) {
 
 	fclose(f);
 
+	uint64_t start_time = get_current_time_us();
 	void* parsed = solution->parse(lines, line_count);
+	printf("Parsing took %ldus\n", get_current_time_us() - start_time);
 
 	printf("part1:\n");
-	uint64_t start_time = get_current_time_us();
+	start_time = get_current_time_us();
 	solution->part1(parsed);
 	printf("Part 1 took %ldus\n\n", get_current_time_us() - start_time);