Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

 

if... else if不要偷懒直接写 if...if...

 

/*** Definition for singly-linked list.* struct ListNode {*     int val;*     ListNode *next;*     ListNode(int x) : val(x), next(NULL) {}* };*/
class Solution {
public:ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {ListNode *head = NULL,*temp = head;if(l1 == NULL && l2 == NULL)return NULL;if(l1 == NULL && l2 != NULL)return l2;if(l1 != NULL && l2 == NULL)return l1;while(l1 != NULL && l2 != NULL){if(l1->val <= l2->val){if(head == NULL){head = l1;temp = head;l1 = l1->next;continue;}temp->next = l1;l1 = l1->next;temp = temp->next;}else if(l1->val > l2->val){if(head == NULL){head = l2;temp = head;l2 = l2->next;continue;}temp->next = l2;l2 = l2->next;temp = temp->next;}}if(l1 == NULL)temp ->next = l2;else if(l2 == NULL)temp ->next =l1;return head;}
};