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/chapter_divide_and_conquer/binary_search_recur.cs

@@ -8,7 +8,7 @@ namespace hello_algo.chapter_divide_and_conquer;
 
 public class binary_search_recur {
     /* 二分查找：问题 f(i, j) */
-    public int DFS(int[] nums, int target, int i, int j) {
+    int DFS(int[] nums, int target, int i, int j) {
         // 若区间为空，代表无目标元素，则返回 -1
         if (i > j) {
             return -1;
@@ -28,7 +28,7 @@ public class binary_search_recur {
     }
 
     /* 二分查找 */
-    public int BinarySearch(int[] nums, int target) {
+    int BinarySearch(int[] nums, int target) {
         int n = nums.Length;
         // 求解问题 f(0, n-1)
         return DFS(nums, target, 0, n - 1);
@@ -37,7 +37,7 @@ public class binary_search_recur {
     [Test]
     public void Test() {
         int target = 6;
-        int[] nums = { 1, 3, 6, 8, 12, 15, 23, 26, 31, 35 };
+        int[] nums = [1, 3, 6, 8, 12, 15, 23, 26, 31, 35];
 
         // 二分查找（双闭区间）
         int index = BinarySearch(nums, target);

codes/csharp/chapter_divide_and_conquer/build_tree.cs

@@ -8,7 +8,7 @@ namespace hello_algo.chapter_divide_and_conquer;
 
 public class build_tree {
     /* 构建二叉树：分治 */
-    public TreeNode DFS(int[] preorder, Dictionary<int, int> inorderMap, int i, int l, int r) {
+    TreeNode? DFS(int[] preorder, Dictionary<int, int> inorderMap, int i, int l, int r) {
         // 子树区间为空时终止
         if (r - l < 0)
             return null;
@@ -25,24 +25,24 @@ public class build_tree {
     }
 
     /* 构建二叉树 */
-    public TreeNode BuildTree(int[] preorder, int[] inorder) {
+    TreeNode? BuildTree(int[] preorder, int[] inorder) {
         // 初始化哈希表，存储 inorder 元素到索引的映射
-        Dictionary<int, int> inorderMap = new();
+        Dictionary<int, int> inorderMap = [];
         for (int i = 0; i < inorder.Length; i++) {
             inorderMap.TryAdd(inorder[i], i);
         }
-        TreeNode root = DFS(preorder, inorderMap, 0, 0, inorder.Length - 1);
+        TreeNode? root = DFS(preorder, inorderMap, 0, 0, inorder.Length - 1);
         return root;
     }
 
     [Test]
     public void Test() {
-        int[] preorder = { 3, 9, 2, 1, 7 };
-        int[] inorder = { 9, 3, 1, 2, 7 };
+        int[] preorder = [3, 9, 2, 1, 7];
+        int[] inorder = [9, 3, 1, 2, 7];
         Console.WriteLine("前序遍历 = " + string.Join(", ", preorder));
         Console.WriteLine("中序遍历 = " + string.Join(", ", inorder));
 
-        TreeNode root = BuildTree(preorder, inorder);
+        TreeNode? root = BuildTree(preorder, inorder);
         Console.WriteLine("构建的二叉树为：");
         PrintUtil.PrintTree(root);
     }

codes/csharp/chapter_divide_and_conquer/hanota.cs

@@ -8,7 +8,7 @@ namespace hello_algo.chapter_divide_and_conquer;
 
 public class hanota {
     /* 移动一个圆盘 */
-    public void Move(List<int> src, List<int> tar) {
+    void Move(List<int> src, List<int> tar) {
         // 从 src 顶部拿出一个圆盘
         int pan = src[^1];
         src.RemoveAt(src.Count - 1);
@@ -17,7 +17,7 @@ public class hanota {
     }
 
     /* 求解汉诺塔：问题 f(i) */
-    public void DFS(int i, List<int> src, List<int> buf, List<int> tar) {
+    void DFS(int i, List<int> src, List<int> buf, List<int> tar) {
         // 若 src 只剩下一个圆盘，则直接将其移到 tar
         if (i == 1) {
             Move(src, tar);
@@ -32,7 +32,7 @@ public class hanota {
     }
 
     /* 求解汉诺塔 */
-    public void SolveHanota(List<int> A, List<int> B, List<int> C) {
+    void SolveHanota(List<int> A, List<int> B, List<int> C) {
         int n = A.Count;
         // 将 A 顶部 n 个圆盘借助 B 移到 C
         DFS(n, A, B, C);
@@ -41,9 +41,9 @@ public class hanota {
     [Test]
     public void Test() {
         // 列表尾部是柱子顶部
-        List<int> A = new() { 5, 4, 3, 2, 1 };
-        List<int> B = new();
-        List<int> C = new();
+        List<int> A = [5, 4, 3, 2, 1];
+        List<int> B = [];
+        List<int> C = [];
         Console.WriteLine("初始状态下：");
         Console.WriteLine("A = " + string.Join(", ", A));
         Console.WriteLine("B = " + string.Join(", ", B));