From 69e43f1bf8bf1abad6f848a46cf40fe4e11c1598 Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Sun, 10 Dec 2023 18:01:02 +0000
Subject: Day 09
---
day09/day09.java | 37 ++++++++++++++++++++++++++++++++++++-
1 file changed, 36 insertions(+), 1 deletion(-)
diff --git a/day09/day09.java b/day09/day09.java
index 4609508..15354cd 100644
--- a/day09/day09.java
+++ b/day09/day09.java
@@ -28,7 +28,18 @@ public class day09 {
}
public static String part2(RandomAccessFile input) throws IOException {
- return "WIP";
+ String line;
+ int sum = 0;
+ while ((line = input.readLine()) != null) {
+ String[] linea = line.split(" ");
+ int[] nums = new int[linea.length];
+ for (int i = 0; i < linea.length; i++) {
+ nums[i] = Integer.parseInt(linea[i]);
+ }
+
+ sum += predictPre(nums);
+ }
+ return Integer.toString(sum);
}
private static int predictNext(int[] line) {
@@ -56,6 +67,30 @@ public class day09 {
return first.get(first.size() - 1);
}
+ private static int predictPre(int[] line) {
+ ArrayList<ArrayList<Integer>> differences = new ArrayList<>();
+ ArrayList<Integer> lastDiffs = new ArrayList<>();
+
+ for (int i: line) {
+ lastDiffs.add(i);
+ }
+
+ differences.add(lastDiffs);
+
+ while (!allZero(lastDiffs)) {
+ lastDiffs = getDifferences(lastDiffs);
+ differences.add(lastDiffs);
+ }
+
+ int temp = 0;
+ for (int i = differences.size() - 2; i >= 0; i--) {
+ ArrayList<Integer> row = differences.get(i);
+ temp = row.get(0) - temp;
+ }
+
+ return temp;
+ }
+
private static boolean allZero(ArrayList<Integer> list) {
for(int i: list) {
if (i != 0) {
--
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