20220401链表：合并两个有序链表

        题目描述：将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。 

        编码实现：

public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        if (null == list1 || null == list2){
            return null == list1?list2:list1;
        }
        ListNode listNode = new ListNode(0);
        ListNode curNode = listNode;
        while (null != list1 && null != list2){
            if (list1.val <= list2.val){
                curNode.next = list1;
                list1 = list1.next;
            }else {
                curNode.next = list2;
                list2 = list2.next;
            }
            curNode = curNode.next;
        }
        curNode.next = null == list1?list2:list1;
        return listNode.next;
    }

    static class ListNode {
      int val;
      ListNode next;
      ListNode() {}
      ListNode(int val) { this.val = val; }
      ListNode(int val, ListNode next) { this.val = val; this.next = next; }
  }