solve day 1

.gitignore

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+build
+input.txt

Makefile

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+main: main.c
+	mkdir -p build
+	gcc -o build/main main.c -lcurl
+
+run: main
+	./build/main

aoc.h

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+#ifndef AOC_H_
+#define AOC_H_
+
+#include <stdbool.h>
+
+typedef int (*solution_cb)(void*);
+typedef struct {
+	int day;
+
+	void* (*parse)(char** lines, int count);
+	int (*part1)(void* data);
+	int (*part2)(void* data);
+} Solution;
+
+// Macro magic for easy of use
+#define ADD_SOLUTION(_day, parse, part1, part2)                                                    \
+		static Solution ptr_##parse;                                                                   \
+		static Solution ptr_##part1;                                                                   \
+		static Solution ptr_##part2                                                                    \
+		__attribute((used, section("g_solutions"))) = {                                                \
+			.parse = parse,                                                                              \
+			.part1 = part1,                                                                              \
+			.part2 = part2,                                                                              \
+			.day = _day                                                                                  \
+		}
+
+#define SOLUTIONS ({                                                                               \
+			extern Solution __start_##g_solutions;                                                       \
+			&__start_##g_solutions;                                                                      \
+		})
+
+#define SOLUTIONS_END ({                                                                           \
+			extern Solution __stop_##g_solutions;                                                        \
+			&__stop_##g_solutions;                                                                       \
+		})
+
+#define SOLUTIONS_COUNT SOLUTIONS_END - SOLUTIONS
+
+#endif //AOC_H_

day1.c

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+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/param.h>
+
+#include "aoc.h"
+
+typedef struct {
+	int *calories;
+	size_t count;
+} Calories;
+
+typedef struct {
+	Calories *elfs;
+	size_t count;
+} Data;
+
+static void *parse(char **lines, int line_count) {
+	int elf_indexes[300] = { 0 };
+	int elf_count = 1;
+	for (int i = 1; i < line_count; i++) {
+		if (strlen(lines[i-1]) == 0) {
+			elf_indexes[elf_count++] = i;
+		}
+	}
+	elf_indexes[elf_count] = line_count+1;
+
+	Data *data = calloc(1, sizeof(Data));
+	data->elfs = calloc(elf_count, sizeof(Calories));
+	data->count = elf_count;
+
+	for (int i = 0; i < elf_count; i++) {
+		int count = (elf_indexes[i+1]-elf_indexes[i])-1;
+		Calories *calories = &data->elfs[i];
+		calories->calories = calloc(count, sizeof(int));
+		calories->count    = count;
+
+		for (int j = 0; j < count; j++) {
+			int line = elf_indexes[i]+j;
+			calories->calories[j] = atoi(lines[line]);
+		}
+	}
+
+	return data;
+}
+
+static int part1(void *p) {
+	Data *data = (Data*)p;
+	int max_calories = 0;
+	for (int i = 0; i < data->count; i++) {
+		int calories = 0;
+		for (int j = 0; j < data->elfs[i].count; j++) {
+			calories += data->elfs[i].calories[j];
+		}
+		max_calories = MAX(max_calories, calories);
+	}
+	return max_calories;
+}
+
+static int part2(void *p) {
+	Data *data = (Data*)p;
+	int max_calories1 = 0;
+	int max_calories2 = 0;
+	int max_calories3 = 0;
+	for (int i = 0; i < data->count; i++) {
+		int calories = 0;
+		for (int j = 0; j < data->elfs[i].count; j++) {
+			calories += data->elfs[i].calories[j];
+		}
+		if (calories > max_calories1) {
+			max_calories3 = max_calories2;
+			max_calories2 = max_calories1;
+			max_calories1 = calories;
+		} else if (calories > max_calories2) {
+			max_calories3 = max_calories2;
+			max_calories2 = calories;
+		} else if(calories > max_calories3) {
+			max_calories3 = calories;
+		}
+	}
+	return max_calories1 + max_calories2 + max_calories3;
+}
+
+ADD_SOLUTION(1, parse, part1, part2);

main.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <curl/curl.h>
+#include <curl/easy.h>
+
+#include "aoc.h"
+
+#include "day1.c"
+
+Solution *find_solution(int day)
+{
+	for (int i = 0; i < SOLUTIONS_COUNT; i++) {
+		Solution *s = &SOLUTIONS[i];
+		if (s->day == day) {
+			return s;
+		}
+	}
+	return NULL;
+}
+
+char **read_lines(int *line_count, FILE *f)
+{
+	*line_count = 0;
+
+	rewind(f);
+	while(!feof(f)){
+		char ch = fgetc(f);
+		if(ch == '\n') {
+			(*line_count)++;
+		}
+	}
+
+	char **lines = malloc(*line_count * sizeof(char*));
+
+	char *line;
+	size_t len = 0;
+	int i = 0;
+	size_t read;
+	rewind(f);
+	while ((read = getline(&line, &len, f)) != -1) {
+		line[read-1] = '\0';
+		lines[i++] = strdup(line);
+	}
+
+	return lines;
+}
+
+int download_input(int day, char *filename, char *session)
+{
+	int rc = 0;
+
+	curl_global_init(CURL_GLOBAL_ALL);
+	FILE *f = fopen(filename, "w");
+	CURL *curl = curl_easy_init();
+
+	CURLcode curl_code;
+	if (curl) {
+		char *cookie_header = calloc(42 + strlen(session), sizeof(char));
+		sprintf(cookie_header, "Cookie: session=%s", session);
+
+		char url[81] = { 0 };
+		sprintf(url, "https://adventofcode.com/2022/day/%d/input", day);
+
+		struct curl_slist *chunk = NULL;
+		chunk = curl_slist_append(chunk, cookie_header);
+
+		curl_easy_setopt(curl, CURLOPT_HTTPHEADER, chunk);
+		curl_easy_setopt(curl, CURLOPT_WRITEDATA, f);
+		curl_easy_setopt(curl, CURLOPT_URL, &url);
+		curl_code = curl_easy_perform(curl);
+		if (curl_code == CURLE_OK) {
+			long http_code = 0;
+			curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &http_code);
+			if (http_code != 200) {
+				fprintf(stderr, "Request failed: HTTP code %ld\n", http_code);
+				rc = -1;
+			}
+		} else {
+			fprintf(stderr, "Request failed: %s\n", curl_easy_strerror(curl_code));
+			rc = -1;
+		}
+
+		curl_easy_cleanup(curl);
+		curl_slist_free_all(chunk);
+	}
+end:
+	curl_global_cleanup();
+	fclose(f);
+	if (rc) {
+		remove(filename);
+	}
+	return rc;
+}
+
+void print_solutions()
+{
+	fprintf(stderr, "Available solutions: ");
+	for (int i = 0; i < SOLUTIONS_COUNT; i++) {
+		Solution *s = &SOLUTIONS[i];
+		fprintf(stderr, "%d ", s->day);
+	}
+	fprintf(stderr, "\n");
+}
+
+int main(int argc, char** argv) {
+	if (argc < 2) {
+		fprintf(stderr, "Usage: %s <day> [input.txt]\n", argv[0]);
+		exit(1);
+	}
+
+	int day = atoi(argv[1]);
+	if (day == 0) {
+		fprintf(stderr, "Day number is invalid\n");
+		print_solutions();
+		exit(1);
+	}
+
+	Solution *solution = find_solution(day);
+	if (solution == NULL) {
+		fprintf(stderr, "Failed to find solution to %d\n", day);
+		print_solutions();
+		exit(1);
+	}
+
+	char *input_file = NULL;
+	if (argc >= 3) {
+		input_file = argv[2];
+	} else if ( access( "input.txt", F_OK ) != -1  ) {
+		input_file = "input.txt";
+	} else {
+		char* session = getenv("AOC_SESSION");
+		if (session && !download_input(1, "input.txt", session)) {
+			input_file = "input.txt";
+		} else {
+			fprintf(stderr, "Missing input file");
+			exit(1);
+		}
+	}
+
+	FILE *f = fopen(input_file, "r");
+	if (f == NULL) {
+		fprintf(stderr, "Failed to open file solution to day '%s': %s\n", input_file, strerror(errno));
+		return 1;
+	}
+
+	int line_count;
+	char **lines = read_lines(&line_count, f);
+
+	fclose(f);
+
+	void* parsed = solution->parse(lines, line_count);
+
+	printf("part1: %d\n", solution->part1(parsed));
+	printf("part2: %d\n", solution->part2(parsed));
+
+	return 0;
+}