2021-advent-12.java

package day12;


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

public class Day12 {


    public Day12() {
        this.t = new HashMap<>();
    }

    private HashMap<String, ArrayList<String>> t;


    void add(String from, String to) {
        if (!from.equals("end") && !to.equals("start")) {
            var currentList = t.get(from);
            if (currentList == null) {
                currentList = new ArrayList<>();
            }
            currentList.add(to);
            t.put(from, currentList);
        }
    }

    public void readInput(String input) throws IOException {
        var lines = Files.readString(Paths.get(input)).split("\n");
        for (int i = 0; i < lines.length; i++) {
            var line = lines[i];
            var tmp = line.split("-");
            add(tmp[0], tmp[1]);
            add(tmp[1], tmp[0]);
        }
    }

    public void prettyPrint() {
        for (var key : t.keySet()) {
            var line = t.get(key);
            System.out.print(key + ": ");
            line.stream().forEach(s -> System.out.print(s + " "));
            System.out.println();
        }
    }

    boolean lowerCaseMaxTwice(String item, ArrayList<String> path) {
        var counts = new HashMap<String, Integer>();
        var wasTwice = false;
        for (var v : path) {
            if (v.equals(v.toLowerCase())) {
                var count = counts.getOrDefault(v, 0);
                count += 1;
                counts.put(v, count);
                if (count.equals(2)) {
                    wasTwice = true;
                }
            }
        }
        if (wasTwice) {
            return counts.getOrDefault(item, 0).equals(0);
        } else {
            return counts.getOrDefault(item, 0) < 2;
        }
    }

    public int step(String node, ArrayList<String> path) {
        var count = 0;
        var moves = t.get(node);
        for (var v : moves) {
            if (!lowerCaseMaxTwice(v, path)) {
                continue;
            }
            if (v.equals("end")) {
                count += 1;
            } else {
                var pathHere = new ArrayList<>(path);
                pathHere.add(v);
                count += step(v, pathHere);
            }
        }
        return count;
    }
}