LeetCode-in-All
24. Swap Nodes in Pairs
Medium
Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list’s nodes (i.e., only nodes themselves may be changed.)
Example 1:
Input: head = [1,2,3,4]
Output: [2,1,4,3]
Example 2:
Input: head = []
Output: []
Example 3:
Input: head = [1]
Output: [1]
Constraints:
- The number of nodes in the list is in the range
[0, 100]. 0 <= Node.val <= 100
Solution
// Definition for singly-linked list.
// 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 swap_pairs(mut head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
let mut dummy = ListNode {
val: 0,
next: head,
};
let mut current = &mut dummy;
while let Some(mut first) = current.next.take() {
if let Some(mut second) = first.next.take() {
first.next = second.next.take();
second.next = Some(first);
current.next = Some(second);
current = current.next.as_mut().unwrap().next.as_mut().unwrap();
} else {
current.next = Some(first);
break;
}
}
dummy.next
}
}