LetCode：707创建链表，我用的双链表，找不出错误在哪，

问题遇到的现象和发生背景

代码：
typedef struct MyLinkList {
int val;
struct MyLinkList *next;
struct MyLinkList *pre;
MyLinkList(): val(-1),pre(NULL),next(NULL){}
MyLinkList(int t): val(t),pre(NULL),next(NULL){}
MyLinkList(int t,MyLinkList *p,MyLinkList *s): val(t),pre(p),next(s){}
}MyLinkedNode;
class MyLinkedList {
private:
MyLinkedNode *head;
MyLinkedNode *tail;
int size;
public:
MyLinkedList() {
head=new MyLinkList(-1);
tail=new MyLinkList(-1);
size=0;
head->next=tail;
tail->pre=head;
}

int get(int index) {
    if(index<0||index>=size) return -1;
    MyLinkedNode *p=head;
    while(index>=0){
        --index;
        p=p->next;
    }
        return p->val;
}

void addAtHead(int val) {
    MyLinkedNode *newNode=new MyLinkList(val,head,head->next);
    head->next->pre=newNode;
    head->next=newNode;
    ++size;
}
void addAtTail(int val) {
    MyLinkedNode *newNode=new MyLinkList(val,tail->pre,tail);
    tail->pre->next=newNode;
    tail->pre=newNode;
    ++size;
}

void addAtIndex(int index, int val) {
    if(index==size){
        addAtTail(val); return;
    }
    else if(index>size)
        return;
    else if(index<0){
        addAtHead(val);
        return;
    }
    MyLinkedNode *p=head;
    while(index>=0){
        --index;
        p=p->next;
    }
    MyLinkedNode *newNode=new MyLinkList(val,p->pre,p);
    p->pre->next=newNode;
    p->pre=newNode;
} 
void deleteAtIndex(int index) {
    if(index<0||index>=size) return;
    MyLinkedNode *p=head;
    while(index>=0){
        --index;
        p=p->next;
    }
    p->pre->next=p->next;
    p->next->pre=p->pre;
    delete(p);
    --size;
}

};