24. Swap Nodes in Pairs

JIAKAOBO

LeetCode

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Problem

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

Code

class Solution {
    public ListNode swapPairs(ListNode head) {
        if(head == null || head.next == null) return head;

        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode curr = dummy;

        while(curr.next != null && curr.next.next != null){
            ListNode first = curr.next;
            ListNode second = curr.next.next;

            curr.next = second;
            first.next = second.next;
            second.next = first;

            curr = curr.next.next;
        }

        return dummy.next;
    }
}