题解 | #合并两个排序的链表#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 * 
 * @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)
        return pHead2;
    if (pHead2 == NULL)
        return pHead1;
    typedef struct ListNode* L;
    L pre = NULL;
    L temp = NULL;
    L newHead = pHead1->val < pHead2->val ? pHead1 : pHead2;
    // 如果有差距大的先排除
    temp = pHead1;
    while (pHead1 && pHead1->val < pHead2->val) {
        pre = pHead1;
        pHead1 = pHead1->next;
    }
    if (pHead1 != temp) 
        pHead1 = pre;
    else {
        temp = pHead2;
        while (pHead2 && pHead1->val > pHead2->val) {
            pre = pHead2;
            pHead2 = pHead2->next;
        }
        if (pHead2 != temp) 
            pHead2 = pre;
    }
    pre = NULL;
    while (pHead1 && pHead2) {
        if (pHead1->val < pHead2->val) {
            if (pre)
                pre->next = pHead1;
            pre = pHead1;
            pHead1 = pHead1->next;
            pre->next = pHead2;
        }
        else {
            if (pre)
                pre->next = pHead2;
            pre = pHead2;
            pHead2 = pHead2->next;
            pre->next = pHead1;
        }
    }
    return newHead;
}