D9: Both parts solved and optimized.

Author: Formula-9

Program.cs

@@ -1,17 +1,16 @@
 using AoCHelper;
-using Formula9.AdventOfCode.Solutions2023.Day08;
-using Formula9.AdventOfCode.Utils;
+using Formula9.AdventOfCode.Solutions2023.Day10;
 
 namespace Formula9.AdventOfCode;
 
 public class Program
 {
  public static void Main(string[] args)
  {
- Type day = typeof(Day_08);
+ Type day = typeof(Day_10);
  // var _d = Activator.CreateInstance(day) as AdventOfCodeProblem;
- //Console.WriteLine(_d.Solve_1().AsTask().Result);
- //Console.WriteLine(_d.Solve_2().AsTask().Result);
+ // Console.WriteLine(_d.Solve_1().AsTask().Result);
+ // Console.WriteLine(_d.Solve_2().AsTask().Result);
  Solver.Solve(options => {
  options.ShowTotalElapsedTimePerDay = false;
  options.ShowOverallResults = false;

Solutions/Day08/Day08.cs

@@ -49,7 +49,6 @@ public override ValueTask<string> Solve_1()
  return new(steps.ToString());
  }
 
- // 20685524831999
  public override ValueTask<string> Solve_2()
  {
  HashSet<string> startPoints = Graph.Where(kvp => kvp.Key.EndsWith("A")).Select(kvp => kvp.Key).ToHashSet();

Solutions/Day09/Day09.cs

@@ -4,9 +4,22 @@ namespace Formula9.AdventOfCode.Solutions2023.Day09;
 
 public class Day_09 : AdventOfCodeProblem
 {
- public Day_09() : base(2023, 09) { }
+ public List<List<long>> Histories { get; init; }
 
- public override ValueTask<string> Solve_1() => new("Solution 1");
+ public Day_09() : base(2023, 09) 
+ { 
+ Histories = Input.SplitByNewline().Select(l => l.Split(" ").Select(long.Parse).ToList()).ToList();
+ }
 
- public override ValueTask<string> Solve_2() => new("Solution 2");
+ public static long Project(IEnumerable<long> values, int indexToExclude)
+ {
+ int n = values.Count();
+ return (long)Math.Round(Enumerable.Range(0, n).Where(n => n != indexToExclude).Product(k => (double)(n - k) / (indexToExclude - k)));
+ }
+
+ public static double LagrangeInterpolatingPolynomial(IEnumerable<long> values) => values.Sum((v, index) => v * Project(values, index));
+ 
+ public override ValueTask<string> Solve_1() => new(Histories.Sum(LagrangeInterpolatingPolynomial).ToString());
+
+ public override ValueTask<string> Solve_2() => new(Histories.Sum(h => LagrangeInterpolatingPolynomial(h.AsEnumerable().Reverse())).ToString());
 }

Utils/EnumerableUtils.cs

@@ -16,13 +16,6 @@ public static bool Any<T>(this IEnumerable<T> source, Func<T, bool> predicate, o
  return false;
  }
 
- public static IEnumerable<T> Sort<T>(this IEnumerable<T> source, IComparer<T> comparer)
- {
- var lst = source.ToList();
- lst.Sort(comparer);
- return lst;
- }
-
  public static long Sum<T>(this IEnumerable<T> source, Func<T, int, long> func)
  {
  long result = 0;
@@ -46,24 +39,11 @@ public static IEnumerable<T> RepeatInfinitely<T>(this IEnumerable<T> source)
  }
  }
 
- public static int Move<T>(this IEnumerator<T> enumerator, int steps)
- {
- for (int i = 0; i < steps; i++)
- {
- if (!enumerator.MoveNext()) return i;
- }
- return steps;
- }
-
- public static IEnumerator<T> Move<T>(this IEnumerator<T> enumerator, int steps, out int stepsMoved)
- {
- stepsMoved = enumerator.Move(steps);
- return enumerator;
- }
-
  public static T Next<T>(this IEnumerator<T> enumerator)
  {
  enumerator.MoveNext();
  return enumerator.Current;
  }
+
+ public static double Product<T>(this IEnumerable<T> values, Func<T, double> keySelector) => values.Aggregate(1d, (acc, el) => acc * keySelector(el));
 }