From 1c879b6b8645a5b22c670f15f989dcbcd479546f Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Fri, 15 Dec 2023 11:28:25 +0000
Subject: Day 15

---
 day15/day15.java | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 day15/day15.java

(limited to 'day15/day15.java')

diff --git a/day15/day15.java b/day15/day15.java
new file mode 100644
index 0000000..5f4a7b5
--- /dev/null
+++ b/day15/day15.java
@@ -0,0 +1,98 @@
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.util.ArrayList;
+import java.util.AbstractMap.SimpleEntry;
+
+public class day15 {
+  public static void main(String args[]) throws IOException {
+    RandomAccessFile input = new RandomAccessFile("input", "r");
+    System.out.println("Day 15 Part 1: " + part1(input));
+    input.seek(0);
+    System.out.println("Day 15 Part 2: " + part2(input));
+    input.close();
+  }
+
+  public static String part1(RandomAccessFile input) throws IOException {
+    String[] init = input.readLine().split(",");
+
+    int sum = 0;
+    for(String s: init) {
+      sum += hash(s);
+    }
+
+    return Integer.toString(sum);
+  }
+
+  public static String part2(RandomAccessFile input) throws IOException {
+    String[] init = input.readLine().split(",");
+    PairList[] boxes = new PairList[256];
+
+    for (int i = 0; i < 256; i++) {
+      boxes[i] = new PairList();
+    }
+
+    for (String cmd: init) {
+      if (cmd.endsWith("-")) {
+        String[] cmda = cmd.split("-");
+        int box = hash(cmda[0]);
+        boxes[box].remove(cmda[0]);
+      } else {
+        String[] cmda = cmd.split("=");
+        int box = hash(cmda[0]);
+        boxes[box].put(cmda[0], Integer.parseInt(cmda[1]));
+      }
+    }
+
+    int sum = 0;
+    for (int i = 0; i < 256; i++) {
+      sum += ((i + 1) * boxes[i].power());
+    }
+
+    return Integer.toString(sum);
+  }
+
+  private static int hash(String s) {
+    int cur = 0;
+    for (int a: s.toCharArray()) {
+      cur += a;
+      cur *= 17;
+      cur %= 256;
+    }
+    return cur;
+  }
+
+  static class PairList {
+    ArrayList<SimpleEntry<String, Integer>> pairlist;
+
+    public PairList() {
+      pairlist = new ArrayList<>();
+    }
+
+    public void remove(String key) {
+      for (int i = 0; i < pairlist.size(); i++) {
+        if (pairlist.get(i).getKey().equals(key)) {
+          pairlist.remove(i);
+          return;
+        }
+      }
+    }
+
+    public void put(String key, Integer value) {
+      for (int i = 0; i < pairlist.size(); i++) {
+        if (pairlist.get(i).getKey().equals(key)) {
+          pairlist.get(i).setValue(value);
+          return;
+        }
+      }
+      pairlist.add(new SimpleEntry(key, value));
+    }
+
+    public int power() {
+      int sum = 0;
+      for (int i = 0; i < pairlist.size(); i++) {
+        sum += ((i + 1) * pairlist.get(i).getValue());
+      }
+      return sum;
+    }
+  }
+}
-- 
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