Creating rotate list

data_structures/linked_list/rotate_list.py

@@ -0,0 +1,38 @@
+"""
+Given a list, rotate the list to the right by k places,
+where k is non-negative.
+For example:
+Given 1->2->3->4->5->NULL and k = 2,
+return 4->5->1->2->3->NULL.
+"""
+
+# Definition for singly-linked list.
+# class ListNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+
+def rotate_right(head, k):
+    """
+    :type head: ListNode
+    :type k: int
+    :rtype: ListNode
+    """
+    if not head or not head.next:
+        return head
+    current = head
+    length = 1
+    # count length of the list
+    while current.next:
+        current = current.next
+        length += 1
+    # make it circular
+    current.next = head
+    k = k % length
+    # rotate until length-k
+    for i in range(length-k):
+        current = current.next
+    head = current.next
+    current.next = None
+    return head