aoc2023/day4/p1.c

80 lines
1.8 KiB
C

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
uint64_t parse_number(char *end);
int main(int argc, char **argv) {
FILE *input;
char *line = NULL;
size_t line_length = 0;
if (argc == 1 || argv[1][0] == '-')
input = stdin;
else if ((input = fopen(argv[1], "r")) == NULL) {
printf("Cannot open file %s\n", argv[1]);
return -1;
}
uint64_t total_points = 0;
size_t winning_numbers_len = 0;
uint8_t *winning_numbers = NULL;
char *colon_pos = NULL, *pipe_pos = NULL;
while (getline(&line, &line_length, input) != -1) {
colon_pos = strchr(line, ':');
pipe_pos = strchr(line, '|');
if (winning_numbers == NULL) {
winning_numbers_len = (pipe_pos - colon_pos - 2) / 3;
winning_numbers = (uint8_t *) calloc(winning_numbers_len, sizeof(uint8_t));
}
for (size_t i = 0, wl_pos = (size_t)colon_pos+4; i < winning_numbers_len; ++i, wl_pos += 3)
winning_numbers[i] = parse_number((char *)(wl_pos-1));
uint64_t points = 0;
for (char *n_pos = pipe_pos + 4;; n_pos += 3) {
uint8_t n = parse_number(n_pos-1);
for (size_t i = 0; i < winning_numbers_len; ++i) {
if (n != winning_numbers[i])
continue;
points = (points == 0) ? 1 : points * 2;
break;
}
if (*n_pos == '\n')
break;
}
total_points += points;
memset(line, 0, line_length);
}
free(winning_numbers);
printf("%lu\n", total_points);
return 0;
}
uint64_t parse_number(char *end) {
uint64_t num = 0;
for (size_t n = 1;; n *= 10) {
if (*end>>4 != 0x3)
break;
num += (*end&0xf) * n;
--end;
}
return num;
}