Solution.java

package toboggantrajectory;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

/**
 * With the toboggan login problems resolved, you set off toward the airport. While travel by toboggan might be easy, it's certainly not safe: there's very minimal steering and the area is covered in trees. You'll need to see which angles will take you near the fewest trees.
 *
 * Due to the local geology, trees in this area only grow on exact integer coordinates in a grid. You make a map (your puzzle input) of the open squares (.) and trees (#) you can see. For example:
 *
 * ..##.......
 * #...#...#..
 * .#....#..#.
 * ..#.#...#.#
 * .#...##..#.
 * ..#.##.....
 * .#.#.#....#
 * .#........#
 * #.##...#...
 * #...##....#
 * .#..#...#.#
 * These aren't the only trees, though; due to something you read about once involving arboreal genetics and biome stability, the same pattern repeats to the right many times:
 *
 * ..##.........##.........##.........##.........##.........##.......  --->
 * #...#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
 * .#....#..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
 * ..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
 * .#...##..#..#...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
 * ..#.##.......#.##.......#.##.......#.##.......#.##.......#.##.....  --->
 * .#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
 * .#........#.#........#.#........#.#........#.#........#.#........#
 * #.##...#...#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...
 * #...##....##...##....##...##....##...##....##...##....##...##....#
 * .#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#  --->
 * You start on the open square (.) in the top-left corner and need to reach the bottom (below the bottom-most row on your map).
 *
 * The toboggan can only follow a few specific slopes (you opted for a cheaper model that prefers rational numbers); start by counting all the trees you would encounter for the slope right 3, down 1:
 *
 * From your starting position at the top-left, check the position that is right 3 and down 1. Then, check the position that is right 3 and down 1 from there, and so on until you go past the bottom of the map.
 *
 * The locations you'd check in the above example are marked here with O where there was an open square and X where there was a tree:
 *
 * ..##.........##.........##.........##.........##.........##.......  --->
 * #..O#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
 * .#....X..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
 * ..#.#...#O#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
 * .#...##..#..X...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
 * ..#.##.......#.X#.......#.##.......#.##.......#.##.......#.##.....  --->
 * .#.#.#....#.#.#.#.O..#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
 * .#........#.#........X.#........#.#........#.#........#.#........#
 * #.##...#...#.##...#...#.X#...#...#.##...#...#.##...#...#.##...#...
 * #...##....##...##....##...#X....##...##....##...##....##...##....#
 * .#..#...#.#.#..#...#.#.#..#...X.#.#..#...#.#.#..#...#.#.#..#...#.#  --->
 * In this example, traversing the map using this slope would cause you to encounter 7 trees.
 *
 * Starting at the top-left corner of your map and following a slope of right 3 and down 1, how many trees would you encounter?
 *
 * --- Part Two ---
 * Time to check the rest of the slopes - you need to minimize the probability of a sudden arboreal stop, after all.
 *
 * Determine the number of trees you would encounter if, for each of the following slopes, you start at the top-left corner and traverse the map all the way to the bottom:
 *
 * Right 1, down 1.
 * Right 3, down 1. (This is the slope you already checked.)
 * Right 5, down 1.
 * Right 7, down 1.
 * Right 1, down 2.
 * In the above example, these slopes would find 2, 7, 3, 4, and 2 tree(s) respectively; multiplied together, these produce the answer 336.
 *
 * What do you get if you multiply together the number of trees encountered on each of the listed slopes?
 */
public class Solution {

    public static void main(String[] args) throws FileNotFoundException {
        FileInputStream fis = new FileInputStream("input.txt");
        Scanner sc = new Scanner(fis);    //file to be scanned
        List<String> items = new ArrayList<>();
        while(sc.hasNextLine())
        {
            items.add(sc.nextLine());
        }
        sc.close();     //closes the scanner

        char[][] map = new char[items.size()][items.get(0).length()];


        for (int i = 0; i < items.size(); i++) {
            map[i] = items.get(i).toCharArray();
        }

        int i11 = countTrees(map, 1, 1);
        int i31 = countTrees(map, 3, 1);
        int i51 = countTrees(map, 5, 1);
        int i71 = countTrees(map, 7, 1);
        int i12 = countTrees(map, 1, 2);

        System.out.println(i11 * i31 * i51 * i71 * i12);
    }

    private static int countTrees(char[][] map, int colAdd, int rowAdd) {

        int[] current = new int[]{0, 0};

        int finalRow  = map.length - 1;
        int patternLength = map[0].length;

        int[] nextCoords = new int[2];

        int count = 0;

        while (current[0] != finalRow) {

            nextCoords[0] = current[0] + rowAdd;
            nextCoords[1] = current[1] + colAdd;

            if (nextCoords[1] > map[0].length - 1) {
                nextCoords[1] = nextCoords[1] - map[0].length;
            }

            if (map[nextCoords[0]][nextCoords[1]] == '#') {
                count ++;
            }

            current[0] = nextCoords[0];
            current[1] = nextCoords[1];
        }

        return count;


    }
}