LeetCode - 24. Swap Nodes in Pairs(LinkedList, Recursion)***

문제

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.)

https://leetcode.com/problems/swap-nodes-in-pairs/

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]

풀이

class Solution {
    public ListNode swapPairs(ListNode head) {
        if(head==null) return head;
        if(head.next==null) return head;
        
        ListNode cur = new ListNode(0);
        cur.next = head;
        ListNode newHead = cur;
    
        while(cur.next!=null&&cur.next.next!=null){
            
            ListNode n1=cur.next;
            ListNode n2=n1.next;
            ListNode next=n2.next;
            
            cur.next=n2;
            n2.next=n1;
            n1.next=next;
            
            cur=n1;
        }
        
        return newHead.next;
    }
}