2018.1.8 LeetCode 21. Merge Two Sorted Lists 【链表的基本运用】

21. Merge Two Sorted Lists

Description

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.

Example:

Input: 1->2->4, 1->3->4

Output: 1->1->2->3->4->4

题意： 合并两个链表

分析： 新建一个链表，然后逐个判断即可，需要注意：

1、是否有头结点

2、l1,l2为空的情况

参考函数

class Solution {
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
if(l1 == NULL) return l2;
if(l2 == NULL) return l1;
ListNode* res = NULL;
if(l1->val >= l2->val) {
res = l2;
l2 = l2->next;
} else {
res = l1;
l1 = l1->next;
}
ListNode* p = res; // point
while (l1 && l2) {
if(l1->val >= l2->val) {
p->next = l2;
l2 = l2->next;
} else {
p->next = l1;
l1 = l1->next;
}
p = p->next;
}
if(l1) {
p->next = l1;
} else {
p->next = l2;
}
return res;
}
};

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