# 61. Rotate List

## 23 Jan 61. Rotate List

Given the `head` of a linked list, rotate the list to the right by `k` places.

Example 1:

```Input: head = [1,2,3,4,5], k = 2
Output: [4,5,1,2,3]
```

Example 2:

```Input: head = [0,1,2], k = 4
Output: [2,0,1]
```

Constraints:

• The number of nodes in the list is in the range `[0, 500]`.
• `-100 <= Node.val <= 100`
• `0 <= k <= 2 * 109`

### 代码

``````class Solution:
def rotateRight(self, head: ListNode, k: int) -> ListNode:
if not head or not head.next:
return head

tail = head
n = 1
while head.next :
head = head.next
n += 1
head.next = tail
head = head.next

for i in range(n - k % n - 1):
head = head.next
res = head.next
head.next = None
return res``````
https://maxming0.github.io/2020/10/07/Rotate-List/

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
def rotateRight(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
if not head or not head.next:
return head
tail = head
n = 1
while head.next:
head = head.next
n += 1

head.next = tail
head = head.next
k = n – k%n – 1
for i in range(k):
head = head.next
result = head.next
head.next = None
return result