day 6

4 files changed, 173 insertions, 1 deletions

diff --git a/06.c b/06.c
new file mode 100644
index 0000000..44f7dc9
--- /dev/null
+++ b/06.c
@@ -0,0 +1,101 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <err.h>
+#include <stdbool.h>
+#include "input.h"
+#include "list.h"
+
+#define INPUT "input/06.txt"
+#define INPUT_SIZE 300L
+#define EXPECTED1 380758L
+#define EXPECTED2 1710623015163L
+
+void part1(struct input_str* input) {
+	char* start = input->lines[0];
+	char* end = start;
+	struct long_list* lanterns = long_list_init(INPUT_SIZE);
+
+	// parse input
+	while(*end != '\n') {
+		long timer = strtol(start, &end, 0);
+		start = end;
+		if(*end == ',')
+			start++;
+
+		long_list_add(lanterns, timer);
+	}
+
+	// time flies
+	for(int day = 0; day < 80; day++) {
+		size_t init_length = lanterns->length; // we should leave alone the new lanterns
+		for(size_t i = 0; i < init_length; i++) {
+			long timer = long_list_get(lanterns, i);
+			if(timer == 0) {
+				timer = 7;
+				long_list_add(lanterns, 8);
+			}
+			timer--;
+			long_list_set(lanterns, i, timer);
+		}
+	}
+
+	CHECK(lanterns->length, EXPECTED1);
+	long_list_free(lanterns);
+}
+
+void part2(struct input_str* input) {
+	// simulating 256 days with the naive approach from part1 is too long and uses up too much memory
+	// we need to count lanternfishes based on their timer
+	long* lantern_count_by_timer = calloc(9, sizeof(long));
+	char* start = input->lines[0];
+	char* end = start;
+
+	// parse input
+	while(*end != '\n') {
+		long timer = strtol(start, &end, 0);
+		start = end;
+		if(*end == ',')
+			start++;
+
+		lantern_count_by_timer[timer]++;
+	}
+
+	long* lantern_count_2 = calloc(9, sizeof(long));
+	for(int day = 0; day < 256; day++) {
+		// simulate the timers decreasing
+		for(int i = 8; i > 0; i--) {
+			lantern_count_2[i-1] = lantern_count_by_timer[i];
+		}
+		// handle special cases of lanternfishes with timer 0
+		lantern_count_2[8] = lantern_count_by_timer[0];
+		lantern_count_2[6] += lantern_count_by_timer[0];
+
+		// switch arrays for the next day
+		long* lantern_count_tmp = lantern_count_by_timer;
+		lantern_count_by_timer = lantern_count_2;
+		lantern_count_2 = lantern_count_tmp;
+	}
+
+	// compute total of lanternfish
+	long sum = 0;
+	for(int i = 0; i < 9; i++)
+		sum += lantern_count_by_timer[i];
+
+	free(lantern_count_by_timer);
+	free(lantern_count_2);
+	CHECK(sum, EXPECTED2);
+}
+
+int main() {
+	// read input
+	struct input_str input;
+	input_str_read(&input, INPUT);
+
+	// do stuff
+	part1(&input);
+	part2(&input);
+
+	// cleanup & exit
+	input_str_free(&input);
+	return 0;
+}
diff --git a/Makefile b/Makefile
index 9f34f8a..97c64b6 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 CC=cc
 CFLAGS=-std=c1x -W -Wall -g
 LDFLAGS=
-EXEC=01 02 03 04 05
+EXEC=01 02 03 04 05 06
 
 all: $(EXEC)
 
@@ -23,5 +23,8 @@ all: $(EXEC)
 05: input.o 05.o
 	$(CC) -o $@ $> $(LDFLAGS)
 
+06: input.o list.o 06.o
+	$(CC) -o $@ $> $(LDFLAGS)
+
 clean:
 	rm -rf *.o $(EXEC)
diff --git a/list.c b/list.c
new file mode 100644
index 0000000..6001424
--- /dev/null
+++ b/list.c
@@ -0,0 +1,46 @@
+#include <err.h>
+#include "list.h"
+
+#define LIST_SIZE 50
+
+struct long_list* long_list_init(size_t size) {
+	struct long_list* list = malloc(sizeof(struct long_list));
+	list->list = malloc(sizeof(long) * size);
+	list->alloc_size = size;
+	list->length = 0;
+	return list;
+}
+
+void long_list_free(struct long_list* list) {
+	if(list == NULL)
+		return;
+
+	if(list->list != NULL)
+		free(list->list);
+
+	free(list);
+}
+
+void long_list_add(struct long_list* list, long value) {
+	// increase space if needed
+	if(list->length >= list->alloc_size) {
+		list->list = realloc(list->list, sizeof(long) * (list->alloc_size + LIST_SIZE));
+		list->alloc_size += LIST_SIZE;
+	}
+	list->list[list->length] = value;
+	list->length = list->length + 1;
+}
+
+long long_list_get(struct long_list* list, size_t index) {
+	if(index >= list->length)
+		err(1, "index %ld out of bounds (%ld)", index, list->length);
+
+	return list->list[index];
+}
+
+void long_list_set(struct long_list* list, size_t index, long value) {
+	if(index >= list->length)
+		err(1, "index %ld out of bounds (%ld)", index, list->length);
+
+	list->list[index] = value;
+}
diff --git a/list.h b/list.h
new file mode 100644
index 0000000..21ceeaa
--- /dev/null
+++ b/list.h
@@ -0,0 +1,22 @@
+#ifndef DEF_LISTH
+#define DEF_LISTH
+
+#include <stdlib.h>
+
+struct long_list {
+	long* list;
+	size_t alloc_size;
+	size_t length;
+};
+
+struct long_list* long_list_init(size_t size);
+
+void long_list_free(struct long_list* list);
+
+void long_list_add(struct long_list* list, long value);
+
+long long_list_get(struct long_list* list, size_t index);
+
+void long_list_set(struct long_list* list, size_t index, long value);
+
+#endif