Merge pull request #2097 from eeee0717/master

添加C#版

problems/0019.删除链表的倒数第N个节点.md

@@ -412,6 +412,28 @@ struct ListNode* removeNthFromEnd(struct ListNode* head, int n) {
 
 ```
 
+C#：
+```csharp
+public class Solution {
+    public ListNode RemoveNthFromEnd(ListNode head, int n) {
+        ListNode dummpHead = new ListNode(0);
+        dummpHead.next = head;
+        var fastNode = dummpHead;
+        var slowNode = dummpHead;
+        while(n-- != 0 && fastNode != null)
+        {
+            fastNode = fastNode.next;
+        }
+        while(fastNode.next != null)
+        {
+            fastNode = fastNode.next;
+            slowNode = slowNode.next;
+        }
+        slowNode.next = slowNode.next.next;
+        return dummpHead.next;
+    }
+}
+```
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problems/0142.环形链表II.md

@@ -437,6 +437,34 @@ object Solution {
 }
 ```
 
+C#:
+```CSharp
+public class Solution
+{
+    public ListNode DetectCycle(ListNode head)
+    {
+        ListNode fast = head;
+        ListNode slow = head;
+        while (fast != null && fast.next != null)
+        {
+            slow = slow.next;
+            fast = fast.next.next;
+            if (fast == slow)
+            {
+                fast = head;
+                while (fast != slow)
+                {
+                    fast = fast.next;
+                    slow = slow.next;
+                }
+                return fast;
+            }
+        }
+        return null;
+    }
+}
+```
+
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problems/0203.移除链表元素.md

@@ -596,6 +596,41 @@ class Solution {
 }
 ```
 
+C#
+```CSharp
+/**
+ * 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 class Solution
+{
+    public ListNode RemoveElements(ListNode head, int val)
+    {
+        ListNode dummyHead = new ListNode(0,head);
+        ListNode temp = dummyHead;
+        while(temp.next != null)
+        {
+            if(temp.next.val == val)
+            {
+                temp.next = temp.next.next;
+            }
+            else
+            {
+                temp = temp.next;
+            }
+        }
+        return dummyHead.next;
+    }
+}
+```
+
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problems/0977.有序数组的平方.md

@@ -488,6 +488,14 @@ public class Solution {
         return result;
     }
 }
+
+C# LINQ：
+```csharp
+public class Solution {
+    public int[] SortedSquares(int[] nums) {
+       return nums.Select(x => x * x).OrderBy(x => x).ToArray();
+    }
+}
 ```
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