Modernize and refactor C# codebase to leverage latest C# features (#545)

Author: Ambaaq-Ajibike

Algorithms/DataCompression/HuffmanCompressor.cs

@@ -21,14 +21,14 @@ public class HuffmanCompressor(IComparisonSorter<HuffmanCompressor.ListNode> sor
     {
         if (string.IsNullOrEmpty(uncompressedText))
         {
-            return (string.Empty, new Dictionary<string, string>());
+            return (string.Empty, []);
         }
 
         if (uncompressedText.Distinct().Count() == 1)
         {
             var dict = new Dictionary<string, string>
             {
-                { "1", uncompressedText[0].ToString() },
+                ["1"] = uncompressedText[0].ToString(),
             };
             return (new string('1', uncompressedText.Length), dict);
         }

Algorithms/Problems/DynamicProgramming/CoinChange/DynamicCoinChangeSolver.cs

@@ -21,7 +21,7 @@ public static int[] GenerateSingleCoinChanges(int coin, int[] coins)
         Array.Sort(coinsArrayCopy);
         Array.Reverse(coinsArrayCopy);
 
-        var list = new List<int>();
+        List<int> list = [];
 
         foreach (var item in coinsArrayCopy)
         {
@@ -50,7 +50,7 @@ public static int[] GenerateSingleCoinChanges(int coin, int[] coins)
     /// <returns>Change dictionary for all values [1,N], where N is the coin.</returns>
     public static Dictionary<int, int[]> GenerateChangesDictionary(int coin, int[] coins)
     {
-        var dict = new Dictionary<int, int[]>();
+        Dictionary<int, int[]> dict = [];
         var currentCoin = 1;
 
         while (currentCoin <= coin)

Algorithms/Problems/TravelingSalesman/TravelingSalesmanSolver.cs

@@ -78,7 +78,7 @@ public static (int[] Route, double Distance) SolveNearestNeighbor(double[,] dist
         }
 
         var visited = new bool[n];
-        var route = new List<int> { start };
+        List<int> route = [start];
         visited[start] = true;
         double totalDistance = 0;
         int current = start;
@@ -120,16 +120,15 @@ private static IEnumerable<int[]> Permute(int[] arr)
         if (arr.Length == 1)
         {
             yield return arr;
+            yield break;
         }
-        else
+
+        for (int i = 0; i < arr.Length; i++)
         {
-            for (int i = 0; i < arr.Length; i++)
+            var rest = arr.Where((_, idx) => idx != i).ToArray();
+            foreach (var perm in Permute(rest))
             {
-                var rest = arr.Where((_, idx) => idx != i).ToArray();
-                foreach (var perm in Permute(rest))
-                {
-                    yield return new[] { arr[i] }.Concat(perm).ToArray();
-                }
+                yield return [arr[i], ..perm];
             }
         }
     }

DataStructures/BinarySearchTree/BinarySearchTree.cs

@@ -316,6 +316,7 @@ private IList<TKey> GetKeysInOrder(BinarySearchTreeNode<TKey>? node)
             return [];
         }
 
+        // Use mutable list approach instead of spread operator for better performance
         var result = new List<TKey>();
         result.AddRange(GetKeysInOrder(node.Left));
         result.Add(node.Key);
@@ -335,6 +336,7 @@ private IList<TKey> GetKeysPreOrder(BinarySearchTreeNode<TKey>? node)
             return [];
         }
 
+        // Use mutable list approach instead of spread operator for better performance
         var result = new List<TKey>
         {
             node.Key,
@@ -356,6 +358,7 @@ private IList<TKey> GetKeysPostOrder(BinarySearchTreeNode<TKey>? node)
             return [];
         }
 
+        // Use mutable list approach instead of spread operator for better performance
         var result = new List<TKey>();
         result.AddRange(GetKeysPostOrder(node.Left));
         result.AddRange(GetKeysPostOrder(node.Right));

DataStructures/Heap/PairingHeap/PairingHeap.cs

@@ -223,7 +223,7 @@ private void Map(T newItem, PairingHeapNode<T> newNode)
         }
         else
         {
-            mapping[newItem] = new List<PairingHeapNode<T>>(new[] { newNode });
+            mapping[newItem] = [newNode];
         }
     }