feat(csharp) .NET 8.0 code migration (#966)

* .net 8.0 migration

* update docs

* revert change

* revert change and update appendix docs

* remove static

* Update binary_search_insertion.cs

* Update binary_search_insertion.cs

* Update binary_search_edge.cs

* Update binary_search_insertion.cs

* Update binary_search_edge.cs

---------

Co-authored-by: Yudong Jin <krahets@163.com>

codes/csharp/utils/ListNode.cs

@@ -5,14 +5,10 @@
 namespace hello_algo.utils;
 
 /* Definition for a singly-linked list node */
-public class ListNode {
-    public int val;
+public class ListNode(int x) {
+    public int val = x;
     public ListNode? next;
 
-    public ListNode(int x) {
-        val = x;
-    }
-
     /* Generate a linked list with an array */
     public static ListNode? ArrToLinkedList(int[] arr) {
         ListNode dum = new(0);
@@ -33,7 +29,7 @@ public class ListNode {
     }
 
     public override string? ToString() {
-        List<string> list = new();
+        List<string> list = [];
         var head = this;
         while (head != null) {
             list.Add(head.val.ToString());

codes/csharp/utils/PrintUtil.cs

@@ -6,14 +6,9 @@
 
 namespace hello_algo.utils;
 
-public class Trunk {
-    public Trunk? prev;
-    public string str;
-
-    public Trunk(Trunk? prev, string str) {
-        this.prev = prev;
-        this.str = str;
-    }
+public class Trunk(Trunk? prev, string str) {
+    public Trunk? prev = prev;
+    public string str = str;
 };
 
 public static class PrintUtil {
@@ -45,8 +40,8 @@ public static class PrintUtil {
     }
 
     /* Print a linked list */
-    public static void PrintLinkedList(ListNode head) {
-        List<string> list = new();
+    public static void PrintLinkedList(ListNode? head) {
+        List<string> list = [];
         while (head != null) {
             list.Add(head.val.ToString());
             head = head.next;
@@ -115,10 +110,10 @@ public static class PrintUtil {
     /* Print a heap */
     public static void PrintHeap(Queue<int> queue) {
         Console.Write("堆的数组表示：");
-        List<int> list = queue.ToList();
+        List<int> list = [.. queue];
         Console.WriteLine(string.Join(',', list));
         Console.WriteLine("堆的树状表示：");
-        TreeNode tree = TreeNode.ListToTree(list.Cast<int?>().ToList());
+        TreeNode? tree = TreeNode.ListToTree(list.Cast<int?>().ToList());
         PrintTree(tree);
     }
 
@@ -126,13 +121,13 @@ public static class PrintUtil {
     public static void PrintHeap(PriorityQueue<int, int> queue) {
         var newQueue = new PriorityQueue<int, int>(queue.UnorderedItems, queue.Comparer);
         Console.Write("堆的数组表示：");
-        List<int> list = new();
+        List<int> list = [];
         while (newQueue.TryDequeue(out int element, out _)) {
             list.Add(element);
         }
         Console.WriteLine("堆的树状表示：");
         Console.WriteLine(string.Join(',', list.ToList()));
-        TreeNode tree = TreeNode.ListToTree(list.Cast<int?>().ToList());
+        TreeNode? tree = TreeNode.ListToTree(list.Cast<int?>().ToList());
         PrintTree(tree);
     }
 }

codes/csharp/utils/TreeNode.cs

@@ -7,17 +7,12 @@
 namespace hello_algo.utils;
 
 /* 二叉树节点类 */
-public class TreeNode {
-    public int val;        // 节点值
-    public int height;     // 节点高度
+public class TreeNode(int? x) {
+    public int? val = x;    // 节点值
+    public int height;      // 节点高度
     public TreeNode? left;  // 左子节点引用
     public TreeNode? right; // 右子节点引用
 
-    /* 构造方法 */
-    public TreeNode(int x) {
-        val = x;
-    }
-
     // 序列化编码规则请参考：
     // https://www.hello-algo.com/chapter_tree/array_representation_of_tree/
     // 二叉树的数组表示：
@@ -35,11 +30,11 @@ public class TreeNode {
     //             \——— 8
 
     /* 将列表反序列化为二叉树：递归 */
-    private static TreeNode? ListToTreeDFS(List<int?> arr, int i) {
+    static TreeNode? ListToTreeDFS(List<int?> arr, int i) {
         if (i < 0 || i >= arr.Count || !arr[i].HasValue) {
             return null;
         }
-        TreeNode root = new(arr[i].Value) {
+        TreeNode root = new(arr[i]) {
             left = ListToTreeDFS(arr, 2 * i + 1),
             right = ListToTreeDFS(arr, 2 * i + 2)
         };
@@ -52,7 +47,7 @@ public class TreeNode {
     }
 
     /* 将二叉树序列化为列表：递归 */
-    private static void TreeToListDFS(TreeNode? root, int i, List<int?> res) {
+    static void TreeToListDFS(TreeNode? root, int i, List<int?> res) {
         if (root == null)
             return;
         while (i >= res.Count) {
@@ -65,7 +60,7 @@ public class TreeNode {
 
     /* 将二叉树序列化为列表 */
     public static List<int?> TreeToList(TreeNode root) {
-        List<int?> res = new();
+        List<int?> res = [];
         TreeToListDFS(root, 0, res);
         return res;
     }

codes/csharp/utils/Vertex.cs

@@ -7,11 +7,8 @@
 namespace hello_algo.utils;
 
 /* 顶点类 */
-public class Vertex {
-    public int val;
-    public Vertex(int val) {
-        this.val = val;
-    }
+public class Vertex(int val) {
+    public int val = val;
 
     /* 输入值列表 vals ，返回顶点列表 vets */
     public static Vertex[] ValsToVets(int[] vals) {
@@ -24,7 +21,7 @@ public class Vertex {
 
     /* 输入顶点列表 vets ，返回值列表 vals */
     public static List<int> VetsToVals(List<Vertex> vets) {
-        List<int> vals = new();
+        List<int> vals = [];
         foreach (Vertex vet in vets) {
             vals.Add(vet.val);
         }