LeetCode | Merge Two Sorted Lists（合并两个链表）

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.

题目解析：

合并链表，很简单，注意好传入为空指针即可。

由于头结点的确定，为了避免在循环中做无谓的比较，直接在while之前先确定头指针。

class Solution {
public:
ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
if(l1 == NULL)
return l2;
if(l2 == NULL)
return l1;
ListNode *head;
if(l1->val < l2->val){
head = l1;
l1 = l1->next;
}else{
head = l2;
l2 = l2->next;
}

ListNode *p = head;
while(l1 && l2){
if(l1->val < l2->val){
p->next = l1;
p = l1;
l1 = l1->next;
}else{
p->next = l2;
p = l2;
l2 = l2->next;
}
}
if(l1 == NULL){
p->next = l2;
}
if(l2 == NULL)
p->next = l1;
return head;
}
};