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#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;
}
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