aoc2023-day1/src/calibration.c

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>

#include "string.h"
#include "io.h"

static char first_digit(char *line) {
    while (*line != '\0' && !isdigit(*line)) {
        line++;
    }

    if (*line != '\0') {
        return *line;
    } else {
        return 0;
    }
}

unsigned int get_calibration_sum(FILE *input_file) {
    unsigned int sum = 0;
    char *current_line, *reversed_line;
    char intermediate_buffer[3];
    intermediate_buffer[2] = '\0';

    while (!feof(input_file)) {
        current_line = read_line(input_file);
        reversed_line = strrev(current_line);
        if (*current_line != '\0') {
            intermediate_buffer[0] = first_digit(current_line);
            intermediate_buffer[1] = first_digit(reversed_line);
            sum += atoi(intermediate_buffer);
        }
        free(reversed_line);
        free(current_line);
    }

    return sum;
}