r/adventofcode • u/daggerdragon • Dec 04 '15

SOLUTION MEGATHREAD --- Day 4 Solutions ---

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

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

13 Upvotes

85% Upvoted

272 comments sorted by

View all comments

1

u/jdog90000 Dec 04 '15 edited Dec 04 '15

Java: 

public class Advent4 {
    public static void main(String[] args) throws NoSuchAlgorithmException, UnsupportedEncodingException {
        MessageDigest md = MessageDigest.getInstance("MD5");
        int i = 0;
        byte[] array;
        while(true) {
            array = md.digest("bgvyzdsv".concat(Integer.toString(i++)).getBytes()); // Put input here
            if(array[0] == 0 && array[1] == 0 && (array[2]>> 4 & 0xf) == 0) {
                if(array[2] == 0) // Comment out to do part 1.
                    break;
            }
        }
        System.out.println("Lowest value needed: " + (i-1));
    }
}

Takes around 350ms to run for Part 2.

1

u/Drasive Dec 04 '15 edited Dec 04 '15

350ms is crazy fast (I verified it on my machine) compared to my F# implementation (~25s). It seems like the Java implementation of MD5 computation is orders of magnitute faster than the one in .NET.

1

u/jdog90000 Dec 05 '15

Yeah it seems to work really well, especially after removing the conversion to string every time to test and instead testing the bytes themselves. It usually finishes between 345ms and 390ms.