AdventOfCode2023/09/09.c

#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>

#define DEFAULT_FILE        "input.txt"
#define STRBUF_LEN          300
#define ISDIGIT(X)          (X >= '0' && X <= '9')
#define NUM_ARR_LEN         300
#define NUM_DIFFS           300

#define REVERSE_ARR         1


bool all_zeroes(int *num_arr, int len)
{
    int i = 0;
    for (i = 0; i < len; i++)
    {
        if (num_arr[i]) return false;
    }
    return true;
}

int parse_num(char *str)
{
    bool isnegative = false;
    if (*str == '-')
    {
        isnegative = true;
        str++;
    }
    uint64_t num = 0;
    while (ISDIGIT(*str))
    {
        num = (num * 10) + (*str - '0');
        str++;
    }
    return isnegative ? -num : num;
}

void reverse_arr(int *num_arr, int len)
{
    int i = 0;
    int temp;
    for (i = 0; i < (len  / 2); i++)
    {
        temp = num_arr[i];
        num_arr[i] = num_arr[len - i - 1];
        num_arr[len - i - 1] = temp;
    }
}

int parse_nums(char *str, int *num_arr)
{
    int i = 0;

    while (*str != '\n')    
    {
        if (*str == ' ') str++;
        num_arr[i] = parse_num(str);
        i++;
        while (ISDIGIT(*str) || *str == '-') str++;
    }


#if (REVERSE_ARR)
    int k = 0;
    int temp;
    for (k = 0; k < (i  / 2); k++)
    {
        temp = num_arr[k];
        num_arr[k] = num_arr[i - k - 1];
        num_arr[i - k - 1] = temp;
    }
#endif

    return i;
}

void print_arr(int *num_arr, int len)
{
    int i = 0;
    for (i = 0; i < len; i++)
    {
        printf("%d ", num_arr[i]);
    }
    printf("\n");
}

void calc_diff(int num_arr_len, int num_arr[num_arr_len], int diff_arr[num_arr_len - 1])
{
    int i = 0;
    for (i = 0; i < (num_arr_len - 1); i++)
    {
        diff_arr[i] = num_arr[i + 1] - num_arr[i];
    }
}

int calc_all_diffs(int diffs_arr[NUM_DIFFS][NUM_ARR_LEN], int lens_arr[NUM_DIFFS])
{
    int k = 0;
    while (!all_zeroes(diffs_arr[k], lens_arr[k]))
    {
        calc_diff(lens_arr[k], diffs_arr[k], diffs_arr[k + 1]);
        lens_arr[k + 1] = lens_arr[k] - 1;
        k++;
    }

    memset(diffs_arr[k], 0, sizeof(int) * NUM_ARR_LEN);

    return k;
}

#define PREDICT_NEXT(num_arr, num_arr_len, diffs) (num_arr[num_arr_len - 1] + diffs[num_arr_len - 1])

int predict_next_val(int diffs_arr[NUM_DIFFS][NUM_ARR_LEN], int *lens_arr, int depth)
{
    while (depth)
    {
        depth--;
        int len = lens_arr[depth];

        int *current_arr = diffs_arr[depth];
        int *diff = diffs_arr[depth + 1];

        int current_arr_last_val = current_arr[len - 1];
        int diff_last_val = diff[len - 1];

        int next = current_arr_last_val + diff_last_val;
        diffs_arr[depth][len] = next;
        print_arr(diffs_arr[depth], lens_arr[depth] + 1);
    }
    return diffs_arr[0][lens_arr[0]];
}

int main(int argc, char **argv)
{
    // Get filename as an argument, if there is one
    char *path = (argc > 1) ? argv[1] : DEFAULT_FILE;

    if (!path)
    {
        printf("Requires input file.\n");
        return 1;
    }

    FILE *file = fopen(path, "r");
    char strbuf[STRBUF_LEN] = {0};

    if (!file)
    {
        printf("Could not find file.");
        return 1;
    }

    // Begin challenge

    // diffs_arr[0] is a single line of the puzzle input
    // diffs_arr[0][0] is the first int of the first line
    int diffs_arr[NUM_DIFFS][NUM_ARR_LEN];

    // Length of each diff arr
    int lens_arr[NUM_DIFFS] = {0};

    int i = 0;
    uint64_t sum = 0;

    while (fgets(strbuf, STRBUF_LEN, file))
    {
        if (strbuf[0] == '\n') break;
        lens_arr[0] = parse_nums(strbuf, diffs_arr[0]);

        int depth = calc_all_diffs(diffs_arr, lens_arr);

        int next_val = predict_next_val(diffs_arr, lens_arr, depth);

        sum += next_val;
    }

    printf("Sum: %lu\n", sum);

    return 0;
}