合并两个链表，将b链表插入a链表报错

Question

class ListNode {
int val;
ListNode next = null;

ListNode(int val) {
    this.val = val;
}

}
public class Solution {
public ListNode Merge(ListNode list1,ListNode list2) {
if(list1 == null) {
return list2;
}
if(list2 == null) {
return list1;
}

ListNode p=list1,q=list2;
     if(p.val>q.val){
        p = list2 ; //p small
        q = list1 ;
    }
    
     ListNode r1= p.next,r2 = q.next ;
 
    while(q!=null){
          if (r1.val >= q.val){
              r2 = q.next ;
              q.next=r1 ;
              p.next=q ;

              p = r1 ;
              r1 = p.next ;
              q = r2 ;

          }else {
              p = r1 ;
              r1 = r1.next ;
             if (r1 == null){
                 p.next = q ;
             }

          }
    }
    return list1;
}

}

Answer 1

这个p不判断空不会空指针吗？还有你这个变量名太随意了，即使有一个链表为空也要合并，可以参考下我写的

    // 合并链表，合并两个有序链表，合并后仍旧有序
    private static LinkList mergeList(LinkList list1, LinkList list2){
        if(list1 == null && list2 == null){
            return null;
        }
 
        LinkList listMerge = new LinkList();
        LinkList resList = listMerge;
 
        while(list1 != null && list2 != null){
            if((Integer)list1.getData() > (Integer) list2.getData()){
                listMerge.setNext(list1);
                list1 = list1.getNext();
            } else{
                listMerge.setNext(list2);
                list2 = list2.getNext();
            }
            listMerge = listMerge.getNext();
        }
        listMerge.setNext(list1 == null? list2 : list1);
 
        return resList;
    }