链表 - 两两交换链表中的节点

24. 链表 - 两两交换链表中的节点

方法一：递归

/**
 * @param {ListNode} head
 * @return {ListNode}
 */
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;
};

方法二：迭代

/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var swapPairs = function (head) {
    const dummyHead = new ListNode(0);
    dummyHead.next = head;
    let temp = dummyHead;
    while (temp.next != null && temp.next.next !== null) {
        const node1 = temp.next;
        const node2 = temp.next.next;
        temp.next = node2;
        node1.next = node2.next;
        node2.next = node1;
        temp = node1;
    }
    return dummyHead.next;
};