力扣707. 设计链表

class MyLinkedList {
public:
    struct LinkedList{
        int val;
        LinkedList * next;
        LinkedList(int val) : val(val), next(nullptr) {}
    };

    MyLinkedList() {
        dummyhead = new LinkedList(-1);
        size = 0;
    }
    
    int get(int index) {
        if(index >= size) {
            return -1;
        }
        LinkedList* cur = dummyhead->next;
        while(index--) {
            cur = cur->next;
        }
        return cur->val;
    }
    
    void addAtHead(int val) {
        LinkedList * newnode = new LinkedList(val);
        newnode->next = dummyhead->next;
        dummyhead->next = newnode;
        size++;
    }
    
    void addAtTail(int val) {
        LinkedList* cur = dummyhead;
        LinkedList* newnode = new LinkedList(val);
        while(cur->next) {
            cur = cur->next;
        }
        newnode->next = cur->next;
        cur->next = newnode;
        size++;
    }
    
    void addAtIndex(int index, int val) {
        if(index > size) {
            return;
        }
        LinkedList* newnode = new LinkedList(val);
        LinkedList* cur = dummyhead;
        while(index--){
            cur = cur->next;
        }
        newnode->next = cur->next;
        cur->next = newnode;
        size++;
    }
    
    void deleteAtIndex(int index) {
        if(index >= size) {
            return;
        }
        LinkedList* cur = dummyhead;
        while(index--){
            cur = cur->next;
        }
        LinkedList* tmp = cur->next;
        cur->next = tmp->next;
        delete tmp;
        tmp = nullptr;
        size--;
    }

private:
    LinkedList * dummyhead;
    int size;
};

/**
 * Your MyLinkedList object will be instantiated and called as such:
 * MyLinkedList* obj = new MyLinkedList();
 * int param_1 = obj->get(index);
 * obj->addAtHead(val);
 * obj->addAtTail(val);
 * obj->addAtIndex(index,val);
 * obj->deleteAtIndex(index);
 */