首先我们使用一种便于理解的方法,将链表一分为二,然后归并排序,再合并两个有序链表。
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* sortList(ListNode* head) {
if(head == nullptr || head->next == nullptr)
return head;
ListNode* slow = head,*fast = head->next;
while(fast && fast->next)
{
slow = slow->next;
fast = fast->next->next;
}
//[slow]-->[---]->[---]
//将链表一分为二
fast = slow->next;
slow->next = nullptr;
return mergeTwoLists(sortList(head),sortList(fast));
}
private:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
ListNode* dummy = new ListNode(-1);
ListNode* p = dummy;
while(l1 && l2)
{
if(l1->val < l2->val)
{
p->next = l1;
l1 = l1->next;
}else{
p->next = l2;
l2 = l2->next;
}
p = p->next;
}
if(l1) p->next = l1;
if(l2) p->next = l2;
return dummy->next;
}
};
实现效率:
Runtime: 192 ms, faster than 6.59% of C++ online submissions for Sort List.
Memory Usage: 48.7 MB, less than 21.99% of C++ online submissions for Sort List.