【leedcode刷题 7】合并两个有序链表
题目
将两个有序链表合并为一个新的有序链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。
示例:
输入:1->2->4, 1->3->4
输出:1->1->2->3->4->4
方法一(递归)
/**
* 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) {
if(l1==NULL)
return l2;
if(l2==NULL)
return l1;
if(l1->val < l2->val)
{
l1->next = mergeTwoLists(l1->next,l2);
return l1;
}
else
{
l2->next = mergeTwoLists(l1,l2->next);
return l2;
}
}
};
方法二(迭代)
/**
* 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* a = new ListNode(-1);
ListNode* b = a;
while(l1 != NULL && l2 != NULL) {
if(l1->val <= l2->val) {
b->next = l1;
l1 = l1->next;
} else {
b->next = l2;
l2 = l2->next;
}
b = b->next;
}
b->next = l1 != NULL ? l1 : l2;
// return a->next;//在堆上开辟的空间,要释放,否则内存泄漏
ListNode* c = a->next;
delete a;
return c;
}
};