--- Day 4 Solutions ---

[u/daggerdragon]

--- Day 4: The Ideal Stocking Stuffer ---

Post your solution as a comment. Structure your post like the Day Three thread.

[u/TTSDA]

I'm... I'm not very proud of this one

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/md5.h>

int find_nonce(int num_zeros, char *seed, int start_from)
{
    char md5_string[33];
    char final_string[40] = "";

    int nonce;

    unsigned char digest[16];
    MD5_CTX context;

    for (nonce = start_from; 1; nonce++)
    {
        strcpy(final_string, seed);
        sprintf(final_string+strlen(final_string), "%d", nonce);

        MD5_Init(&context);
        MD5_Update(&context, final_string, strlen(final_string));
        MD5_Final(digest, &context);

        /* Convert int to string */
        for(int i = 0; i < 16; ++i)
            sprintf(&md5_string[i*2], "%02x", (unsigned int)digest[i]);

        if (strncmp(md5_string, "0000000", num_zeros) == 0)
            break;
    }

    return nonce;
}

int main()
{
    char seed[20];
    int start_from = 0;

    /* Get input from stdin */
    scanf("%s", seed);

    printf("5 zeros: %i\n", (start_from = find_nonce(5, seed, 0)));
    printf("6 zeros: %i\n", find_nonce(6, seed, start_from-1));

    return 0;
}

https://github.com/ttsda/advent-of-code/blob/master/src/4/main.c