LeetCode Sort List

Sort a linked list in the time of O (nlogn .. It is obvious to use merge or quick sort.

The first time I knew that the original merger could also be written using a linked list, I was brushed down to three views ..... Use the speed pointer method to find the demarcation point.

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:ListNode *getMid(ListNode *head){ListNode *slow=head;ListNode *fast=head;while(fast->next!=NULL&&fast->next->next!=NULL){slow=slow->next;fast=fast->next;fast=fast->next;}return slow;}    ListNode *sortList(ListNode *head)     {    if(head==NULL||head->next==NULL)    {    return head;    }    ListNode *mid=getMid(head);    ListNode *next=mid->next;    mid->next=NULL;    return mergeList(sortList(head),sortList(next));    }    ListNode *mergeList(ListNode *a,ListNode *b)    {    ListNode *tmphead=new ListNode(-1);    ListNode *cur=tmphead;    while(a&&b)    {    if(a->val<=b->val)    {    cur->next=a;    a=a->next;    }    else    {    cur->next=b;    b=b->next;    }    cur=cur->next;    }    cur->next=NULL;    cur->next= a==NULL?b:a;    cur=tmphead->next;    delete tmphead;    return cur;    }};