2022.03.30-第66题-24. 两两交换链表中的节点

[icodeish]

https://leetcode-cn.com/problems/swap-nodes-in-pairs/ 给你一个链表，两两交换其中相邻的节点，并返回交换后链表的头节点。你必须在不修改节点内部的值的情况下完成本题（即，只能进行节点交换）。

 

示例 1： 输入：head = [1,2,3,4] 输出：[2,1,4,3] 示例 2：

输入：head = [] 输出：[] 示例 3：

输入：head = [1] 输出：[1]

[yanggengzhen123]

function swapPairs(head: ListNode | null): ListNode | null {
    if(!head) return null
    let listNode = new ListNode()
    listNode.next = head
    let current = listNode
    while(current.next !== null && current.next.next !== null){
        let n1 = current.next
        let n2 = current.next.next
        current.next = n2
        n1.next = n2.next
        n2.next = n1
        current = current = current.next.next
    }
    return listNode.next
};

[icodeish]

var swapPairs = function (head) {
    if (head === null || head.next === null) {
        return head
    }
    const newHead = head.next
    head.next = swapPairs(newHead.next)
    newHead.next = head
    return newHead
}

[BambooSword]

var swapPairs = function(head) {
    // solution 3 -> iteration
    if(!head || !head.next) return head;
    const dummyHead = new ListNode(0);
    dummyHead.next = head;
    let temp = dummyHead;
    while(temp && temp.next && temp.next.next) {
        list1 = temp.next;
        list2 = temp.next.next;
        list1.next = list2.next;
        temp.next = list2;
        list2.next = list1;
        temp = list1
    }
    return dummyHead.next;
};