Day4

142. Linked List Cycle II/142. Linked List Cycle II.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <RootNamespace>_142._Linked_List_Cycle_II</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

142. Linked List Cycle II/ListNode.cs

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+namespace _142._Linked_List_Cycle_II;
+
+//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);
+    }
+}

142. Linked List Cycle II/Program.cs

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+namespace _142._Linked_List_Cycle_II
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            var l1 = new ListNode(3);
+            var l2 = new ListNode(2);
+
+            l1.next = l2;
+            l2.next = l1;
+            Console.WriteLine(new Solution().DetectCycle(l1)?.val);
+        }
+    }
+}

142. Linked List Cycle II/Solution.cs

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+namespace _142._Linked_List_Cycle_II;
+
+public class Solution
+{
+    public ListNode? DetectCycle(ListNode head)
+    {
+        ListNode? cur = head;
+        int bit = 1 << 28;
+        int curAbs = 0;
+        while (cur!=null && (curAbs & bit) == 0)
+        {
+            cur.val ^= bit;
+            cur = cur.next;
+            if(cur != null)
+                curAbs = cur.val < 0 ? (cur.val * -1) : cur.val;
+        }
+        cur = head;
+        curAbs = cur.val < 0 ? (cur.val * -1) : cur.val;
+        while (cur != null && (curAbs & bit) != 0)
+        {
+            cur.val ^= bit;
+            cur = cur.next;
+            if (cur != null)
+                curAbs = cur.val < 0 ? (cur.val * -1) : cur.val;
+        }
+        return cur;
+    }
+}