leetcode 148 sortlist

原题：

Sort a linked list in O(n log n) time using constant space complexity.

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Seen this question in a real interview before?   

Yes

 

然而我把快排写完了才发现超时了。。。

真是悲剧。。。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
//快速排序
struct ListNode* sortList(struct ListNode* head) {
    int length=0;
    struct ListNode* p;
    p=head;
    while(p!=NULL)
    {
        length++;
        p=p->next;
    }
    //printf("%d",length);
    struct ListNode* sort(struct ListNode* head,int length);
    return sort(head,length);
}
struct ListNode* sort(struct ListNode* head,int length)
{
    if(length<2)
        return head;
    int left=0;
    int temp=head->val;
    //printf("temp:%d",temp);
    struct ListNode* p,*flag;
    flag=head;
    p=head;
    int orilength=length;
    while(length>1)
    {
        if(p->next->val<temp)
        {
            struct ListNode* pCon;
            pCon=p->next;
            p->next=p->next->next;
            left++;
            pCon->next=head;
            head=pCon;
        }
        else
        {
            p=p->next;
        }
        length--;
    }
    //printf("left:%d",left);
    head=sort(head,left);
    flag->next=sort(flag->next,orilength-left-1);
    //printf("head->val:%d",head->val);
    return head;
}

看了分析，说是应该用归并排序。。。

那我等有空了再补一发吧。