61.rs

// Definition for singly-linked list.
struct Solution();
#[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>>, k: i32) -> Option<Box<ListNode>> {
        // rust 链表无法成环，拆成两个链表再连接
        if head.is_none() {
            return head;
        }
        let mut len = 0;
        let mut head_refer = &head;
        while head_refer.as_ref().is_some() {
            // 记录链表长度
            len += 1;
            head_refer = &head_refer.as_ref()?.next;
        }
        let offset = k % len;
        if offset == 0 {
            return head;
        }
        let mut head_mut_refer = &mut head;
        while len - offset != 1 {
            len -= 1;
            head_mut_refer = &mut head_mut_refer.as_mut()?.next;
        }
        // right = 4->5  head = 1->2->3
        let mut right = head_mut_refer.as_mut()?.next.take();
        let mut right_mut_refer = &mut right;
        while right_mut_refer.as_ref()?.next.is_some() {
            // 找到 right 的尾部
            right_mut_refer = &mut right_mut_refer.as_mut()?.next;
        }
        right_mut_refer.as_mut()?.next = head;
        right
    }
}

fn main(){
    println!("{:?}",Solution::rotate_right(
        Some(Box::new(ListNode{val:1,next:Some(Box::new(ListNode{val:2,next:Some(Box::new(ListNode{val:3,next:Some(Box::new(ListNode{val:4,next:Some(Box::new(ListNode{val:5,next:None}))}))}))}))})),2
    ));
}