From a09db7c49822168c90c5c48477e434f32d7bf9ba Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Tue, 12 Dec 2023 01:05:41 +0000
Subject: Day 11 part 2

---
 day11/day11.java | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 75 insertions(+), 1 deletion(-)

diff --git a/day11/day11.java b/day11/day11.java
index 6bf7c19..2fd9f8a 100644
--- a/day11/day11.java
+++ b/day11/day11.java
@@ -68,7 +68,43 @@ public class day11 {
   }
 
   public static String part2(RandomAccessFile input) throws IOException {
-    return "WIP";
+    ArrayList<Integer[]> galaxies = new ArrayList<>();
+
+    String line;
+    int h = 0;
+    int w = 0;
+    while ((line = input.readLine()) != null) {
+      w = 0;
+      for (char ch: line.toCharArray()) {
+        if (ch == '#') {
+          galaxies.add(new Integer[] {h, w});
+        }
+        w += 1;
+      }
+      h += 1;
+    }
+
+    for (int r = h - 1; r >= 0; r--) {
+      if (rowEmpty(galaxies, r)) {
+        moveDown(galaxies, r, 999999);
+      }
+    }
+
+    for (int c = w - 1; c >= 0; c--) {
+      if (colEmpty(galaxies, c)) {
+        moveRight(galaxies, c, 999999);
+      }
+    }
+
+    long sum = 0;
+
+    for (int i = 0; i < galaxies.size() - 1; i++) {
+      for (int j = i + 1; j < galaxies.size(); j++) {
+        sum += longDist(galaxies.get(i), galaxies.get(j));
+      }
+    }
+
+    return Long.toString(sum);
   }
 
   static enum Pixel {
@@ -88,4 +124,42 @@ public class day11 {
   private static int dist(Integer[] i, Integer[] j) {
     return Math.abs(i[0] - j[0]) + Math.abs(i[1] - j[1]);
   }
+
+  private static long longDist(Integer[] i, Integer[] j) {
+    return Math.abs(i[0] - j[0]) + Math.abs(i[1] - j[1]);
+  }
+
+  private static boolean rowEmpty(ArrayList<Integer[]> galaxies, int row) {
+    for (Integer[] galaxy: galaxies) {
+      if (galaxy[0] == row) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private static void moveDown(ArrayList<Integer[]> galaxies, int row, int dist) {
+    for (Integer[] galaxy: galaxies) {
+      if (galaxy[0] > row) {
+        galaxy[0] += dist;
+      }
+    }
+  }
+
+  private static boolean colEmpty(ArrayList<Integer[]> galaxies, int col) {
+    for (Integer[] galaxy: galaxies) {
+      if (galaxy[1] == col) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private static void moveRight(ArrayList<Integer[]> galaxies, int col, int dist) {
+    for (Integer[] galaxy: galaxies) {
+      if (galaxy[1] > col) {
+        galaxy[1] += dist;
+      }
+    }
+  }
 }
-- 
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