1 files changed, 245 insertions, 0 deletions
diff --git a/day16/day16.java b/day16/day16.java
new file mode 100644
index 0000000..ce07fda
--- /dev/null
+++ b/day16/day16.java
@@ -0,0 +1,245 @@
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.util.ArrayList;
+import java.util.LinkedList;
+
+public class day16 {
+  public static void main(String args[]) throws IOException {
+    RandomAccessFile input = new RandomAccessFile("input", "r");
+    System.out.println("Day 16 Part 1: " + part1(input));
+    input.seek(0);
+    System.out.println("Day 16 Part 2: " + part2(input));
+    input.close();
+  }
+
+  public static String part1(RandomAccessFile input) throws IOException {
+    Grid grid = new Grid();
+
+    String line;
+    while ((line = input.readLine()) != null) {
+      grid.addRow(line);
+    }
+
+    LinkedList<Beam> beams = new LinkedList<>();
+    beams.add(new Beam(0, 0, Dir.Right, grid));
+
+    int count = 500000;
+    while (beams.size() > 0 && count > 0) {
+      Beam beam = beams.remove();
+      LinkedList<Beam> splits = beam.stepThrough();
+      beams.addAll(splits);
+      count -= 1;
+    }
+
+    return Integer.toString(grid.visited());
+  }
+
+  public static String part2(RandomAccessFile input) throws IOException {
+    return "WIP";
+  }
+
+  private static enum Tile {
+    Mirror,
+    BackMirror,
+    VSplitter,
+    HSplitter,
+    Empty
+  }
+
+  private static enum Dir {
+    Right,
+    Left,
+    Up,
+    Down
+  }
+
+  private static class Cell {
+    Tile tile;
+    boolean visited;
+
+    public Cell(Tile tile) {
+      this.tile = tile;
+      this.visited = false;
+    }
+
+    public void visit() {
+      this.visited = true;
+    }
+  }
+
+  private static class Grid {
+    ArrayList<ArrayList<Cell>> grid;
+
+    public Grid() {
+      this.grid = new ArrayList<>();
+    }
+
+    public int rows() {
+      return this.grid.size();
+    }
+
+    public int cols() {
+      return this.grid.get(0).size();
+    }
+
+    public Cell cellAt(int row, int col) {
+      return this.grid.get(row).get(col);
+    }
+
+    public int visited() {
+      int v = 0;
+      for (ArrayList<Cell> row: this.grid) {
+        for (Cell col: row) {
+          if (col.visited) {
+            v += 1;
+          }
+        }
+      }
+      return v;
+    }
+
+    public void addRow(String line) {
+      ArrayList<Cell> row = new ArrayList<>();
+      for (char ch: line.toCharArray()) {
+        switch (ch) {
+          case '/':
+            row.add(new Cell(Tile.Mirror));
+            break;
+          case '\\':
+            row.add(new Cell(Tile.BackMirror));
+            break;
+          case '|':
+            row.add(new Cell(Tile.VSplitter));
+            break;
+          case '-':
+            row.add(new Cell(Tile.HSplitter));
+            break;
+          case '.':
+            row.add(new Cell(Tile.Empty));
+            break;
+        }
+      }
+      this.grid.add(row);
+    }
+  }
+
+  private static class Beam {
+    int row, col;
+    Dir dir;
+    Grid grid;
+
+    public Beam(int row, int col, Dir dir, Grid grid) {
+      this.row = row;
+      this.col = col;
+      this.dir = dir;
+      this.grid = grid;
+    }
+
+    public boolean escaped() {
+      return this.row < 0 ||
+             this.row >= this.grid.rows() ||
+             this.col < 0 ||
+             this.col >= this.grid.cols();
+    }
+
+    public LinkedList<Beam> stepThrough() {
+      LinkedList<Beam> splits = new LinkedList<>();
+
+      while (!this.escaped()) {
+        Cell cell = this.grid.cellAt(this.row, this.col);
+        cell.visit();
+        switch (cell.tile) {
+          case Mirror:
+            switch (this.dir) {
+              case Right:
+                this.dir = Dir.Up;
+                this.row -= 1;
+                break;
+              case Left:
+                this.dir = Dir.Down;
+                this.row += 1;
+                break;
+              case Up:
+                this.dir = Dir.Right;
+                this.col += 1;
+                break;
+              case Down:
+                this.dir = Dir.Left;
+                this.col -= 1;
+                break;
+            }
+            break;
+          case BackMirror:
+            switch (this.dir) {
+              case Right:
+                this.dir = Dir.Down;
+                this.row += 1;
+                break;
+              case Left:
+                this.dir = Dir.Up;
+                this.row -= 1;
+                break;
+              case Up:
+                this.dir = Dir.Left;
+                this.col -= 1;
+                break;
+              case Down:
+                this.dir = Dir.Right;
+                this.col += 1;
+                break;
+            }
+            break;
+          case VSplitter:
+            switch (this.dir) {
+              case Right:
+              case Left:
+                splits.add(new Beam(this.row + 1, this.col, Dir.Down, this.grid));
+                this.dir = Dir.Up;
+                this.row -= 1;
+                break;
+              case Up:
+                this.row -= 1;
+                break;
+              case Down:
+                this.row += 1;
+                break;
+            }
+            break;
+          case HSplitter:
+            switch (this.dir) {
+              case Right:
+                this.col += 1;
+                break;
+              case Left:
+                this.col -= 1;
+                break;
+              case Up:
+              case Down:
+                splits.add(new Beam(this.row, this.col + 1, Dir.Right, this.grid));
+                this.dir = Dir.Left;
+                this.col -= 1;
+                break;
+            }
+            break;
+          default:
+            switch (this.dir) {
+              case Right:
+                this.col += 1;
+                break;
+              case Left:
+                this.col -= 1;
+                break;
+              case Up:
+                this.row -= 1;
+                break;
+              case Down:
+                this.row += 1;
+                break;
+            }
+        }
+      }
+
+      return splits;
+    }
+  }
+}