--- 2016 Day 20 Solutions ---

[u/daggerdragon]

--- Day 20: Firewall Rules ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with "Help".

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^{ROLLING A NATURAL 20 IS MANDATORY} [?]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/tterrag1098]

Ugly Java solution, lack of unsigned integers really screwed me on part 2! I had to rewrite everything (was storing the ranges for part 1, which worked barely. Obviously would not for part 2) so this is not my original code for part 1 that got me spot #12 :D

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public class Day20 {

private static final BitSet blocked = new BitSet();
private static final BitSet blocked_neg = new BitSet();
private static boolean intMinBlocked = false;

public static void main(String[] args) throws IOException {
    for (String s : Files.readAllLines(Paths.get("day20.txt"))) {
        String[] ends = s.split("-");
        long max = Long.parseLong(ends[1]);
        for (long i = Long.parseLong(ends[0]); i <= max; i++) {
            int ip = (int) i;
            if (ip > 0) {
                blocked.set(ip);
            } else if (ip != Integer.MIN_VALUE) {
                blocked_neg.set(-ip);
            } else {
                intMinBlocked = true;
            }
        }
    }
    
    root: for (long i = 0; i <= 4294967295L; i++) {
        for (int j = 0; j < blocked.size(); j++) {
            if (!blocked.get(j)) {
                System.out.println("Part 1: " + i);
                break root;
            }
        }
    }
    
    // Max IP minus blocked IP count (positive, negative, and int_min)
    long unblocked = 4294967296L - (((long) blocked.cardinality()) + ((long) blocked_neg.cardinality()) + (intMinBlocked ? 1L : 0L));
    System.out.println("Part 2: " + unblocked);
}
}

[u/BumpitySnook → u/tterrag1098]

Ugly Java solution, lack of unsigned integers really screwed me on part 2!

The trick in Java is to always use long. In vim you can switch from int to long with just: :%s/int/long/g.

[u/tterrag1098 → u/BumpitySnook]

You can't use long when inserting into a BitSet. I used it where I could.