leetcode 148
思路1:我把它存到数组里让标准库来排序了。。。
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* sortList(ListNode* head) {
vector<int> xx;
ListNode *temp = head;
while(temp)
{
xx.push_back(temp->val);
temp = temp->next;
}
sort(xx.begin(),xx.end());
temp = head;
int i = 0;
while(temp)
{
temp->val = xx[i];
temp = temp->next;
i++;
}
return head;
}
};
思路2:自己实现归并排序
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *sortList(ListNode *head) {
if (head == NULL || head->next == NULL)
return head;
//利用快慢指针将链表分成两部分
ListNode *fast = head, *slow = head;
while (fast->next != NULL && fast->next->next != NULL)
{
fast = fast->next->next;
slow = slow->next;
}
fast = slow;
slow = slow->next;
fast->next = NULL;
ListNode *l1 = sortList(head);
ListNode *l2 = sortList(slow);
return mergeTwoLists(l1, l2);
}
//将两个链表连起来
ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
ListNode dummy(-1);
for (ListNode* p = &dummy; l1 != nullptr || l2 != nullptr; p = p->next)
{
int val1 = l1 == nullptr ? INT_MAX : l1->val;
int val2 = l2 == nullptr ? INT_MAX : l2->val;
if (val1 <= val2)
{
p->next = l1;
l1 = l1->next;
}
else
{
p->next = l2;
l2 = l2->next;
}
}
return dummy.next;
}
};