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 && pHead2 == NULL) {
        return NULL;
    }
    if (pHead1 == NULL && pHead2 != NULL) {
        return pHead2;
    }
    if (pHead1 != NULL && pHead2 == NULL) {
        return pHead1;
    }
    struct ListNode* new = NULL;
    struct ListNode* temp1 = NULL;
    struct ListNode* temp2 = NULL;

    if (pHead1->val <= pHead2->val) {
        new = pHead1;
    } else {
        new = pHead2;
    }
    while (pHead1 != NULL && pHead2 != NULL) {
        if (pHead1->val <= pHead2->val) {
            if (pHead1->val <= pHead2->val && pHead1->next!=NULL&&pHead1->next->val <= pHead2->val) {
                pHead1 = pHead1->next;
            } else {             
                temp1 = pHead1->next;
                pHead1->next = pHead2;
                pHead1 = temp1;
            }
        } else {
            if (pHead2->val < pHead1->val && pHead2->next!=NULL&& pHead2->next->val < pHead1->val) {
                pHead2 = pHead2->next;
            }else{
                temp2 = pHead2->next;
                pHead2->next = pHead1;
                pHead2 = temp2;
            }           
        }
    }
    return new;
}

运行逻辑如下：

注意：当pHead1->val<pHead2->val时，要比较pHead1->next->val与pHead2->val来确认新pHead1是指向pHead2还是指向自己的next

原本的都是递增的