From a6e24c6c2a2ba4337de3ed70633844f11ed6575b Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Sun, 10 Dec 2023 23:12:16 +0000
Subject: Day 10 part 2

---
 day10/day10.java | 195 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 195 insertions(+)
 create mode 100644 day10/day10.java

(limited to 'day10/day10.java')

diff --git a/day10/day10.java b/day10/day10.java
new file mode 100644
index 0000000..c25fffc
--- /dev/null
+++ b/day10/day10.java
@@ -0,0 +1,195 @@
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.util.ArrayList;
+
+public class day10 {
+  public static void main(String args[]) throws IOException {
+    RandomAccessFile input = new RandomAccessFile("input", "r");
+    System.out.println("Day 10 Part 1: " + part1(input));
+    input.seek(0);
+    System.out.println("Day 10 Part 2: " + part2(input));
+    input.close();
+  }
+
+  public static String part1(RandomAccessFile input) throws IOException {
+    int srow = -1, scol = -1;
+    ArrayList<ArrayList<Tile>> grid = new ArrayList<>();
+    String line;
+
+    while ((line = input.readLine()) != null) {
+      ArrayList<Tile> row = new ArrayList<>();
+      grid.add(row);
+      for (char ch: line.toCharArray()) {
+        switch (ch) {
+          case '|':
+            row.add(Tile.Vertical);
+            break;
+          case '-':
+            row.add(Tile.Horizontal);
+            break;
+          case 'L':
+            row.add(Tile.LBend);
+            break;
+          case 'J':
+            row.add(Tile.JBend);
+            break;
+          case '7':
+            row.add(Tile.SBend);
+            break;
+          case 'F':
+            row.add(Tile.FBend);
+            break;
+          case '.':
+            row.add(Tile.Ground);
+            break;
+          case 'S':
+            row.add(Tile.Start);
+            srow = grid.size() - 1;
+            scol = row.size() - 1;
+        }
+      }
+    }
+
+    boolean upcon = false, leftcon = false,
+            downcon = false, rightcon = false;
+
+    if (srow > 0) {
+      Tile t = grid.get(srow - 1).get(scol);
+      if (t == Tile.Vertical || t == Tile.SBend || t == Tile.FBend) {
+        upcon = true;
+      }
+    }
+
+    if (scol > 0) {
+      Tile t = grid.get(srow).get(scol - 1);
+      if (t == Tile.Horizontal || t == Tile.LBend || t == Tile.FBend) {
+        leftcon = true;
+      }
+    }
+
+    if (srow < (grid.size() - 1)) {
+      Tile t = grid.get(srow + 1).get(scol);
+      if (t == Tile.Vertical || t == Tile.LBend || t == Tile.JBend) {
+        downcon = true;
+      }
+    }
+
+    if (scol < (grid.get(0).size() - 1)) {
+      Tile t = grid.get(srow).get(scol + 1);
+      if (t == Tile.Horizontal || t == Tile.JBend || t == Tile.SBend) {
+        rightcon = true;
+      
+      }
+    }
+
+    Follower fa, fb;
+    if (upcon && rightcon) {
+      grid.get(srow).set(scol, Tile.LBend);
+      fa = new Follower(grid, srow, scol, Dir.Up);
+      fb = new Follower(grid, srow, scol, Dir.Right);
+    } else if (upcon && downcon) {
+      grid.get(srow).set(scol, Tile.Vertical);
+      fa = new Follower(grid, srow, scol, Dir.Up);
+      fb = new Follower(grid, srow, scol, Dir.Down);
+    } else if (upcon && leftcon) {
+      grid.get(srow).set(scol, Tile.JBend);
+      fa = new Follower(grid, srow, scol, Dir.Up);
+      fb = new Follower(grid, srow, scol, Dir.Left);
+    } else if (rightcon && downcon) {
+      grid.get(srow).set(scol, Tile.FBend);
+      fa = new Follower(grid, srow, scol, Dir.Right);
+      fb = new Follower(grid, srow, scol, Dir.Down);
+    } else if (rightcon && leftcon) {
+      grid.get(srow).set(scol, Tile.Horizontal);
+      fa = new Follower(grid, srow, scol, Dir.Right);
+      fb = new Follower(grid, srow, scol, Dir.Left);
+    } else if (downcon && leftcon) {
+      grid.get(srow).set(scol, Tile.SBend);
+      fa = new Follower(grid, srow, scol, Dir.Down);
+      fb = new Follower(grid, srow, scol, Dir.Left);
+    } else {
+      System.out.println("ERROR");
+      fa = null;
+      fb = null;
+    }
+
+    fa.step();
+    fb.step();
+
+    int length = 1;
+    while (!(fa.row == fb.row && fa.col == fb.col)) {
+      fa.step();
+      fb.step();
+      length += 1;
+    }
+
+    return Integer.toString(length);
+  }
+
+  public static String part2(RandomAccessFile input) throws IOException {
+    return "WIP";
+  }
+
+  static enum Tile {
+    Vertical,
+    Horizontal,
+    LBend,
+    JBend,
+    SBend,
+    FBend,
+    Ground,
+    Start
+  }
+
+  static enum Dir {
+    Up,
+    Down,
+    Left,
+    Right
+  }
+
+  static class Follower {
+    ArrayList<ArrayList<Tile>> grid;
+    int row, col;
+    Dir dir;
+
+    public Follower(ArrayList<ArrayList<Tile>> grid, int row, int col, Dir dir) {
+      this.grid = grid;
+      this.row = row;
+      this.col = col;
+      this.dir = dir;
+    }
+
+    public void step() {
+      if (this.dir == Dir.Up) {
+        this.row -= 1;
+      } else if (this.dir == Dir.Down) {
+        this.row += 1;
+      } else if (this.dir == Dir.Left) {
+        this.col -= 1;
+      } else if (this.dir == Dir.Right) {
+        this.col += 1;
+      }
+
+      Tile t = this.grid.get(this.row).get(this.col);
+
+      if (t == Tile.LBend && this.dir == Dir.Down) {
+        this.dir = Dir.Right;
+      } else if (t == Tile.LBend && this.dir == Dir.Left) {
+        this.dir = Dir.Up;
+      } else if (t == Tile.JBend && this.dir == Dir.Down) {
+        this.dir = Dir.Left;
+      } else if (t == Tile.JBend && this.dir == Dir.Right) {
+        this.dir = Dir.Up;
+      } else if (t == Tile.SBend && this.dir == Dir.Up) {
+        this.dir = Dir.Left;
+      } else if (t == Tile.SBend && this.dir == Dir.Right) {
+        this.dir = Dir.Down;
+      } else if (t == Tile.FBend && this.dir == Dir.Up) {
+        this.dir = Dir.Right;
+      } else if (t == Tile.FBend && this.dir == Dir.Left) {
+        this.dir = Dir.Down;
+      }
+    }
+  }
+}
-- 
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