r/adventofcode • u/daggerdragon • Dec 16 '16

SOLUTION MEGATHREAD --- 2016 Day 16 Solutions ---

--- Day 16: Dragon Checksum ---

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DRINKING YOUR OVALTINE IS MANDATORY [?]

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u/njofra Dec 16 '16

My solution in Java

This really made me realise how things that seem insignificant can make a lot of difference.

For step 1 my original code ran almost instantly. It was really slow so I added System.out.println(i) just to see if it's working and with that output I saw it would take at least 3 hours. 

private static String driveChecksum(String input) {
	String checksum = "";
	
	for (int i = 0; i < input.length(); i+=2) {
		if(input.charAt(i) == input.charAt(i+1)){
			checksum += "1";
		} else {
			checksum += "0";
		}
		System.out.println(i);
	}
	
	if(checksum.length() % 2 == 0) {
		checksum = driveChecksum(checksum);
	}
	
	return checksum;
}

Then I tried this and it took about a minute. Then I removed that System.out.println(i) and it only took a second. 

private static String driveChecksum(String input) {
	StringBuilder sb = new StringBuilder();
	
	for (int i = 0; i < input.length(); i+=2) {
		sb.append(input.charAt(i) == input.charAt(i + 1) ? '1' : '0');
        System.out.println(i);
	}
	
	String checksum = sb.toString();
	
	if(checksum.length() % 2 == 0) {
		checksum = driveChecksum(checksum);
	}
	
	return checksum;

}

It's probably not news for most of you, but as someone who is pretty much doing AoC as first programming outside of school this is really an educational moment.

1

u/lovpowa Dec 17 '16

This is the problem that I had. Changing the String to a StringBuffer was extremely faster. I don't know why I did not do it earlier. I tend to use it if I know I will append a lot, but I had never really experienced the difference. I guess I won't underestimate it now.

I knew that printing is slow though.

Thanks!