Created
December 3, 2022 06:27
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Advent of Code Day 3 Part 2
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#include <fcntl.h> | |
#include <stdbool.h> | |
#include <stdlib.h> | |
#include <stdint.h> | |
#include <stdio.h> | |
#include <string.h> | |
#include <unistd.h> | |
static char get_priority(char c) | |
{ | |
if (c >= 'a' && c <= 'z') { | |
return c - 96; | |
} else if (c >= 'A' && c <= 'Z') { | |
return c - 38; | |
} else { | |
fprintf(stderr, "Invalid input\n"); | |
exit(-1); | |
} | |
} | |
int main(void) | |
{ | |
int fd = open("input", O_RDONLY); | |
if (fd == -1) { | |
perror("open"); | |
return -1; | |
} | |
char buffer[4096]; | |
ssize_t bytes; | |
size_t answer = 0; | |
uint64_t bitfield[3]; | |
int rucksack = 0; | |
memset(bitfield, 0, 3 * sizeof(uint64_t)); | |
while((bytes = read(fd, buffer, 4096)) > 0) { | |
for (ssize_t i = 0; i < bytes; i++) { | |
if (buffer[i] == '\n') { | |
rucksack++; | |
if (rucksack > 2) { | |
rucksack = 0; | |
uint64_t priority = bitfield[0] & bitfield[1] & bitfield[2]; | |
for (int j = 1; j < 53; j++) { | |
uint64_t test = (uint64_t)1 << j; | |
if (test & priority) { | |
answer += j; | |
break; | |
} | |
} | |
memset(bitfield, 0, 3 * sizeof(uint64_t)); | |
} | |
} else { | |
bitfield[rucksack] |= (uint64_t)1 << get_priority(buffer[i]); | |
} | |
} | |
} | |
printf("Answer: %ld\n", answer); | |
return 0; | |
} |
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