add Rotate List

Author: v-lili

CodeClearWar/61. Rotate List.cs

@@ -0,0 +1,34 @@
+/*
+The basic idea is to link the tail of the list with the head, make it a cycle. Then count to the rotate point and cut it.
+O(n) runtime, O(1) space.
+ */
+public class Solution {
+    public ListNode RotateRight(ListNode head, int k) {
+        if (head == null || head.next == null) return head;
+        // get length
+        int len = 1;
+        ListNode tail = head;
+        while (tail.next != null) {
+            tail = tail.next;
+            len++;
+        }
+        // connect circle
+        tail.next = head;
+        // find new head;
+        var n = len - k % len;
+        while (n > 0) {
+            tail = head;
+            head = head.next;
+            n--;
+        }
+        // cut before the new head
+        tail.next = null;
+        return head;
+    }
+}
+
+/*
+Similar Questions 
+Rotate Array
+Split Linked List in Parts
+ */

LeetcodeCShaprDotNetCore/Solution.cs

@@ -6,17 +6,30 @@ namespace LeetcodeCShaprDotNetCore
 {
     public class Solution
     {
-        public bool IsPalindrome(string s)
+        public ListNode RotateRight(ListNode head, int k)
         {
-            int left = 0, right = s.Length - 1;
-            while (left < right)
+            if (head == null || head.next == null) return head;
+            // get length
+            int len = 1;
+            ListNode tail = head;
+            while (tail.next != null)
             {
-                while (left < right && !char.IsLetterOrDigit(s[left])) left++;
-                while (left < right && !char.IsLetterOrDigit(s[right])) right--;
-                if (char.ToLower(s[left]) != char.ToLower(s[right])) return false;
-                left++; right--;
+                tail = tail.next;
+                len++;
             }
-            return true;
+            // connect circle
+            tail.next = head;
+            // find new head;
+            var n = len - k % len;
+            while (n > 0)
+            {
+                tail = head;
+                head = head.next;
+                n--;
+            }
+            // cut before the new head
+            tail.next = null;
+            return head;
         }
     }
 }