From 918618e0fdcd40b08b3746c69ed1806e202e17c4 Mon Sep 17 00:00:00 2001
From: Xander Sigler <alexander@siglerdev.us>
Date: Sun, 10 Dec 2023 21:35:10 -0800
Subject: [PATCH] Added day 9

---
 AdventOfCode/_2023/Day9.cs | 106 +++++++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)
 create mode 100644 AdventOfCode/_2023/Day9.cs

diff --git a/AdventOfCode/_2023/Day9.cs b/AdventOfCode/_2023/Day9.cs
new file mode 100644
index 0000000..556d9e7
--- /dev/null
+++ b/AdventOfCode/_2023/Day9.cs
@@ -0,0 +1,106 @@
+using AdventOfCode.Common;
+using AdventOfCode.Models;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace AdventOfCode._2023
+{
+    public class Day9 : AOCDay
+    {
+      
+        protected override AOCResponse ExecutePartA()
+        {
+            long total = 0;
+            foreach(var input in this.GetSplitInput())
+            {
+                var listOfValues = input.Split(' ').Select(x => long.Parse(x)).ToList();
+                var entry = new Entry()
+                {
+                    Values = listOfValues
+                };
+                entry.CreateBelowRecord(this._request.Version);
+                if (this._request.Version == AOCVersion.A)
+                {
+                    total += entry.Values.Last();
+                }
+                else
+                {
+                    total += entry.Values.First();
+                }
+                
+                Log( "Result is : \n " +entry.GetPrint());
+            }
+            this.Answer = total;
+            return this._response;
+        }
+
+        protected override AOCResponse ExecutePartB()
+        {
+            return ExecutePartA();
+        }
+    }
+
+    class Entry
+    {
+        public Entry Above { get; set; }
+        public Entry Below { get; set; }
+        public List<long> Values { get; set; }
+
+        public void CreateBelowRecord(AOCVersion version)
+        {
+            var belowValues = new List<long>();
+            for (int i = 0; i < Values.Count-1; i++)
+            {
+                belowValues.Add(Values[i + 1] - Values[i]);
+            }
+            Below = new Entry()
+            {
+                Above = this,
+                Values = belowValues
+            };
+
+            //If the below record we just created consists of all 0s
+            if (Below.IsBottom())
+            {
+                if (version == AOCVersion.A)
+                {
+                    Below.Values.Add(0); //Extrapolated value
+                    var currentAbove = this;
+                    while (currentAbove != null)
+                    {
+                        currentAbove.Values.Add(currentAbove.Values.Last() + currentAbove.Below.Values.Last());
+                        currentAbove = currentAbove.Above;
+                    }
+                }
+                else //Means it is part B
+                {
+                    Below.Values.Insert(0, 0); //Append the 0 to the start
+                    var currentAbove = this;
+                    while (currentAbove != null)
+                    {
+                        currentAbove.Values.Insert(0, currentAbove.Values.First() - currentAbove.Below.Values.First());
+                        currentAbove = currentAbove.Above;
+                    }
+                }
+
+            }
+            else
+            {
+                Below.CreateBelowRecord(version);
+            }
+        }
+
+        public bool IsBottom()
+        {
+            return Values.TrueForAll(x => x == 0);
+        }
+
+        public string GetPrint()
+        {
+            return string.Join(" ", Values)  + "\n " + (Below != null ? Below.GetPrint() : "");
+        }
+    }
+
+}