【链表】21.合并两个有序链表

题目

法1：迭代法

class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        if (list1 == null) {
            return list2;
        } else if (list2 == null) {
            return list1;
        }
        ListNode dummy = new ListNode(-1);
        ListNode cur = dummy;
        while (list1 != null && list2 != null) {
            if (list1.val <= list2.val) {
                cur.next = list1;
                list1 = list1.next;
            } else {
                cur.next = list2;
                list2 = list2.next;
            }
            cur = cur.next;
        }

        if (list1 == null) {
            cur.next = list2;
        } else if (list2 == null) {
            cur.next = list1;
        }

        return dummy.next;
    }
}