Leetcode024-swapNodesInPairs

Description

Given a linked list, swap every two adjacent nodes and return its head.

You may not modify the values in the list’s nodes, only nodes itself may be changed.

Example

Given 1->2->3->4, you should return the list as 2->1->4->3.

Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode swapPairs(ListNode head) {
        if (head == null || head.next == null) return head;
        
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode cur = dummy;
        while(cur.next != null && cur.next.next != null){
            ListNode first = cur.next;
            ListNode second = cur.next.next;
            first.next = second.next;
            cur.next = second;
            second.next = first;
            cur = cur.next.next;
        }
        return dummy.next;
    }
}

---