practice/sort Linkedlist at master · daizhenyang/practice · GitHub

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ListNode* merge(ListNode *a,ListNode *b)
{
    ListNode *h=NULL,*ptr=NULL;
    while (a&&b)
    {
        if (a->val<=b->val)
        {
            if (!h)h=ptr=a;
            else
            {
                ptr->next=a;
                ptr=a;
            }
            a=a->next;
        }
        else
        {
            if (!h)h=ptr=b;
            else
            {
                ptr->next=b;
                ptr=b;
            }
            b=b->next;
        }
    }
    if (a)ptr->next=a;
    else ptr->next=b;
    return h;
}
ListNode* sortLinkList(ListNode *head) {
    int l=0;
    ListNode *p=head;
    while (p)
    {
        l++;
        p=p->next;
    }
    if (l<=1)return head;
    l/=2;l--;
    p=head;
    while (l--)p=p->next;
    ListNode *t=p->next;
    p->next=NULL;
    head=sortLinkList(head);
    t=sortLinkList(t);
    return merge(head,t);
}