Day10.java

import java.io.IO;

import com.horstmann.adventofcode.*;

CharGrid grid;
long sum1;
long sum2;

void parse(Path p) throws IOException {
    grid = CharGrid.parse(p);
    sum1 = 0;
    sum2 = 0;
}

Set<Location> neighbors(Location l) {
    return grid.mainNeighbors(l).stream().filter(p -> grid.get(p) == grid.get(l) + 1).collect(Collectors.toSet());
}

Object part1() {
    var zeroes = grid.findAll('0').toList();
    var nines = grid.findAll('9').toList();
    for (var start : zeroes)
        for (var end : nines) {
            int count = Graphs.simplePaths(start, end, this::neighbors).size();
            if (count >= 1) sum1++;
            sum2 += count;
        }
    return sum1;
}

Object part2() {
    return sum2;
}

void main() throws IOException {
    Util.time(() -> {
        parse(Util.inputPath("a"));
        IO.println(part1());
        IO.println(part2());
        parse(Util.inputPath("z"));
        IO.println(part1());
        IO.println(part2());
    });
}