Rotate List
<p>Given the <code>head</code> of a linked&nbsp;list, rotate the list to the right by <code>k</code> places.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0000-0099/0061.Rotate%20List/images/rotate1.jpg" style="width: 450px; height: 191px;" />
<pre>
<strong>Input:</strong> head = [1,2,3,4,5], k = 2
<strong>Output:</strong> [4,5,1,2,3]
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0000-0099/0061.Rotate%20List/images/roate2.jpg" style="width: 305px; height: 350px;" />
<pre>
<strong>Input:</strong> head = [0,1,2], k = 4
<strong>Output:</strong> [2,0,1]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the list is in the range <code>[0, 500]</code>.</li>
	<li><code>-100 &lt;= Node.val &lt;= 100</code></li>
	<li><code>0 &lt;= k &lt;= 2 * 10<sup>9</sup></code></li>
</ul>
Linked List; Two Pointers
// Definition for singly-linked list.
// #[derive(PartialEq, Eq, Clone, Debug)]
// pub struct ListNode {
//   pub val: i32,
//   pub next: Option<Box<ListNode>>
// }
//
// impl ListNode {
//   #[inline]
//   fn new(val: i32) -> Self {
//     ListNode {
//       next: None,
//       val
//     }
//   }
// }
impl Solution {
    pub fn rotate_right(mut head: Option<Box<ListNode>>, mut k: i32) -> Option<Box<ListNode>> {
        if head.is_none() || k == 0 {
            return head;
        }
        let n = {
            let mut cur = &head;
            let mut res = 0;
            while cur.is_some() {
                cur = &cur.as_ref().unwrap().next;
                res += 1;
            }
            res
        };
        k = k % n;
        if k == 0 {
            return head;
        }

        let mut cur = &mut head;
        for _ in 0..n - k - 1 {
            cur = &mut cur.as_mut().unwrap().next;
        }
        let mut res = cur.as_mut().unwrap().next.take();
        cur = &mut res;
        while cur.is_some() {
            cur = &mut cur.as_mut().unwrap().next;
        }
        *cur = head.take();
        res
    }
}
