AOC10.java

package aoc;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.Map;

public class Day10 {

	public static void main(String[] args) throws IOException {
		int[] vals = Files.readAllLines(Paths.get("input10.txt")).stream().mapToInt(n -> Integer.parseInt(n)).sorted().toArray();
		int n1 = 0;
		int n3 = 1; // counting the device too, it's a 3 difference
		int prev = 0;
		for (int i = 0; i < vals.length; i++) {
			int diff = vals[i]-prev;
			if(diff==1) n1++;
			if(diff==3) n3++;
			if(diff>3) throw new RuntimeException("hole!");
			prev = vals[i];
		}
		System.out.println(n1*n3);
		
		long n = countFrom(vals, -1, new HashMap<>()); // -1 since we start from the plug
		System.out.println(n);
	}

	private static long countFrom(int[] vals, int pos, Map<Integer, Long> calculated) {
		long res = 0;
		if(calculated.containsKey(pos))
		{
			res = calculated.get(pos);
		}
		else
		{
			int val = pos <0 ? 0 : vals[pos];
			for (int i = pos+1; i < vals.length; i++) {
				int v2 = vals[i];
				if(v2-val <= 3) 
				{
					res += countFrom(vals, i, calculated);
				}
				else
				{
					break;
				}
			}
			if(pos==(vals.length-1))
			{
				res++;
			}
			
			System.out.println("putting "+pos+" "+res);
			calculated.put(pos, res);
		}
		return res;
	}

}