编辑代码

#include <stdio.h>
typedef struct ListNode ListNode;

struct ListNode* mergeTwoLists(struct ListNode* list1, struct ListNode* list2)
{
    ListNode* cur1 = list1;
    ListNode* beforecur1 = NULL;
    ListNode* cur2 = list2;
    if (cur2 == NULL)
    {
        return list1;
    }
    while (cur1 && cur2)
    {
        if (cur1->val > cur2->val)
        {
            if (beforecur1 == NULL)
            {
                list2 = cur2->next;
                cur2->next = list1;
                beforecur1 = cur2;
                list1 = cur2;
                cur2 = list2;
            }
            else
            {
                list2 = cur2->next;
                beforecur1->next = cur2;
                beforecur1 = cur2;
                cur2->next = cur1;
                cur2 = list2;
            }
        }
        else
        {
            beforecur1 = cur1;
            cur1 = cur1->next;
        }
    }
    if (cur2)
    {
        if (beforecur1 == NULL)
        {
            list1 = cur2;
        }
        else
        {
            beforecur1->next = cur2;
        }
    }
    return list1;
}