[21] 合并两个有序链表

details

var mergeTwoLists = function (list1, list2) {
    let dummy = new ListNode(0);
    let cur = dummy;

    while (list1 && list2) {
        if (list1.val < list2.val) {
            cur.next = list1;
            list1 = list1.next;
        } else {
            cur.next = list2;
            list2 = list2.next;
        }
        cur = cur.next;
    }

    let left = list1 || list2;
    cur.next = left;

    return dummy.next;
};