Create csharp LinkedList and its unit test.

codes/csharp/chapter_array_and_linkedlist/LinkedList.cs

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+// File: LinkedList.cs
+// Created Time: 2022-12-16
+// Author: mingXta (1195669834@qq.com)
+
+using hello_algo.include;
+
+namespace hello_algo.chapter_array_and_linkedlist
+{
+    public class LinkedList
+    {
+        /// <summary>
+        ///在链表的结点 n0 之后插入结点 P
+        /// </summary>
+        public static void Insert(ListNode n0, ListNode P)
+        {
+            ListNode n1 = n0.next;
+            n0.next = P;
+            P.next = n1;
+        }
+
+        /// <summary>
+        /// 删除链表的结点 n0 之后的首个结点
+        /// </summary>
+        public static void Remove(ListNode n0)
+        {
+            if (n0.next == null)
+                return;
+            // n0 -> P -> n1
+            ListNode P = n0.next;
+            ListNode n1 = P.next;
+            n0.next = n1;
+        }
+
+        /// <summary>
+        ///访问链表中索引为 index 的结点
+        /// </summary>
+        public static ListNode Access(ListNode head, int index)
+        {
+            for (int i = 0; i < index; i++)
+            {
+                head = head.next;
+                if (head == null)
+                    return null;
+            }
+            return head;
+        }
+
+        /// <summary>
+        /// 在链表中查找值为 target 的首个结点
+        /// </summary>
+        public static int Find(ListNode head, int target)
+        {
+            int index = 0;
+            while (head != null)
+            {
+                if (head.val == target)
+                    return index;
+                head = head.next;
+                index++;
+            }
+            return -1;
+        }
+    }
+}