Day3. Start Algorithm

206. Reverse Linked List/206. Reverse Linked List.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <RootNamespace>_206._Reverse_Linked_List</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

206. Reverse Linked List/ListNode.cs

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+namespace _206._Reverse_Linked_List;
+//Definition for singly-linked list.
+public class ListNode
+{
+    public int val;
+    public ListNode? next;
+    public ListNode(int val = 0, ListNode? next = null)
+    {
+        this.val = val;
+        this.next = next;
+    }
+
+    public static ListNode Create(int[] nums)
+    {
+        ListNode l = new ListNode(nums[0]);
+        ListNode cur = l;
+        for (int i = 1; i < nums.Length; i++)
+        {
+            cur.next = new ListNode(nums[i]);
+            cur = cur.next;
+        }
+        return l;
+    }
+
+    public override string ToString()
+    {
+        List<int> list = new List<int>();
+        ListNode? cur = this;
+        while (cur != null)
+        {
+            list.Add(cur.val);
+            cur = cur.next;
+        }
+        return String.Join(" ", list);
+    }
+}

206. Reverse Linked List/Program.cs

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+namespace _206._Reverse_Linked_List
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            var l = ListNode.Create(new int[] { 1 });
+            Console.WriteLine(new Solution().ReverseList(l));
+        }
+    }
+}

206. Reverse Linked List/Solution.cs

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+namespace _206._Reverse_Linked_List;
+
+public class Solution
+{
+    public ListNode? ReverseList(ListNode head)
+    {
+        if (head == null || head.next == null)
+            return head;
+        ListNode cur = head;
+        ListNode newHead = cur.next!;
+        cur.next = null;
+        while (true)
+        {
+            ListNode? buf = newHead.next;
+            newHead.next = cur;
+            if (buf == null)
+                return newHead;
+            cur = newHead;
+            newHead = buf;
+        }
+    }
+}