题解 | #合并两个排序的链表#

我是一个很喜欢分类讨论的人

 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 *
 * C语言声明定义全局变量请加上static，防止重复定义
 *
 * C语言声明定义全局变量请加上static，防止重复定义
 */

/**
 * 
 * @param pHead1 ListNode类 
 * @param pHead2 ListNode类 
 * @return ListNode类
 */
struct ListNode* Merge(struct ListNode* pHead1, struct ListNode* pHead2 ) {
    // write code here
    if(pHead1 == NULL & pHead2 ==NULL)
    {
        return pHead1;
    }
    if(pHead1 == NULL & pHead2 !=NULL)
    {
        return pHead2;
    }
    if(pHead1 != NULL & pHead2 ==NULL)
    {
        return pHead1;
    }
    struct ListNode* p0;
    struct ListNode* p1;
    struct ListNode* p2;
    struct ListNode* p3;
    p0 = NULL;
    p1 = pHead1;
    p2 = pHead2;
    p3 = NULL;
    if(p1->val <= p2->val)
    {
        p0 = p1;
        if(p1->next == NULL)
        {
            p0->next = p2;
            return p0;
        }
        else
        {
            p1 = p1->next;
        }
    }
    else
    {
        p0 = p2;
        if(p2->next == NULL)
        {
            p0->next = p1;
            return p0;
        }
        else
        {
            p2 = p2->next;
        }
    }
    p3 = p0;
    while(p1!=NULL & p2!=NULL)
    {
        if(p1->val <= p2->val)
        {
            p0->next = p1;
            p0 = p1;
            if(p1->next != NULL)
            {
                p1 = p1->next;
            }
            else
            {
                p1->next = p2;
                return p3;
            }
        }
        else
        {
            p0->next = p2;
            p0 = p2;
            if(p2->next != NULL)
            {
                p2 = p2->next;
            }
            else
            {
                p2->next = p1;
                return p3;
            }
        }
    }
    return p3;
}