leecode.147. 对无头结点链表进行插入排序

void InsertSort(struct ListNode* L){
    struct ListNode *p = L->next,*pre=NULL;
    struct ListNode *r = p->next;
    p->next = NULL;
    p = r;
    while(p!=NULL){
        r = p->next;
        pre = L;
        while(pre->next!=NULL && pre->next->val<p->val){
            pre = pre->next;
        }
        p->next = pre->next;
        pre->next = p;
        p = r;
    }
}

struct ListNode* insertionSortList(struct ListNode* head) {
    if(head==NULL) return head;
    struct ListNode* L = (struct ListNode*)malloc(sizeof(struct ListNode)); //借一个头节点
    L->next = head;
    InsertSort(L);
    head = L->next;
    free(L); //还一个头结点
    return head;
}