Swap nodes in pairs

Linked List Recursion

69.0% acceptance

Jan 12, 2026

13072

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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.)

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn swap_pairs(head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
    match head {
      None => None,
      Some(mut first) => {
        match first.next.take() {
          None => Some(first),
          Some(mut second) => {
            first.next = Self::swap_pairs(second.next.take());
            second.next = Some(first);
            Some(second)
          }
        }
      }
    }
  }
}