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snarkbait/Day25.java

Created December 25, 2017 06:03
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  1. snarkbait created this gist Dec 25, 2017.
    101 changes: 101 additions & 0 deletions Day25.java
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,101 @@
    package Advent2017;

    import util.AdventOfCode;

    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    import java.util.function.Function;

    public class Day25 extends AdventOfCode {

    private Map<Integer, Boolean> tape;
    private int position;
    private State current;

    enum State {
    A(State::tlfr, State::reverse),
    B(State::trlf, State::reverse),
    C(State::tlfr, State::reverse),
    D(pos -> -1, bit -> true),
    E(pos -> 1, bit -> false),
    F(pos -> 1, bit -> true);

    Function<Boolean, Integer> nextPos;
    Function<Boolean, Boolean> nextBit;
    State zero;
    State one;

    static {
    A.zero = B;
    A.one = B;
    B.zero = C;
    B.one = E;
    C.zero = E;
    C.one = D;
    D.zero = A;
    D.one = A;
    E.zero = A;
    E.one = F;
    F.zero = E;
    F.one = A;
    }

    State(Function<Boolean, Integer> nextPos, Function<Boolean, Boolean> nextBit) {
    this.nextPos = nextPos;
    this.nextBit = nextBit;
    }

    State next(boolean bit) { return bit ? one : zero; }
    static boolean reverse(boolean bit) {
    return !bit;
    }

    static int trlf(boolean bit) {
    return bit ? 1 : -1;
    }

    static int tlfr(boolean bit) { return bit ? -1 : 1; }

    }

    public Day25(List<String> input) {
    super(input);
    part1Description = "Checksum after 12861455 steps: ";
    part2Description = "No part 2 today! Merry Christmas, Everyone!!";
    }

    @Override
    public Object part1() {
    for (int i = 0; i < 12861455; i++) {
    machineStep();
    }
    return getOnes();
    }

    private void machineStep() {
    boolean bit = tape.getOrDefault(position, false);
    tape.put(position, current.nextBit.apply(bit));
    position += current.nextPos.apply(bit);
    current = current.next(bit);
    }

    private int getOnes() {
    return (int) tape.entrySet().stream()
    .filter(Map.Entry::getValue)
    .count();
    }

    @Override
    public Object part2() {
    return "";
    }

    @Override
    public void parse() {
    tape = new HashMap<>();
    tape.put(0, false);
    current = State.A;
    }

    }