[Leetcode]设计链表

题目

 

代码 

typedef struct SingleList {
public:	
    int val;
	SingleList* next;
    
};
class MyLinkedList {
public:
    /** Initialize your data structure here. */
    MyLinkedList():_head(new SingleList()) {
      
    }
    
    /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
    int get(int index) {
        if(_head->next==nullptr)
            return -1;
        int pos=0;
        auto ptr=_head->next;
        while(ptr!=nullptr)
        {
            if(pos==index)
                return ptr->val;
            else
            {
                ptr=ptr->next;
                pos++;
            }
        }
        return -1;
            
    }
    
    /** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */
    void addAtHead(int val) {
        //如果链表为空
        if(_head->next==nullptr)
        {
            _head->next=new SingleList();
            _head->next->val=val;
        }else
        {
            auto first=_head->next;
            auto newNode=new SingleList();
            newNode->val=val;
            _head->next=newNode;
            newNode->next=first;
        }
        
    }
    
    /** Append a node of value val to the last element of the linked list. */
    void addAtTail(int val) {
        auto i=_head;
        //找到链表尾部
        while(i->next!=nullptr)
            i=i->next;
        i->next=new SingleList();
        i->next->val=val;
    }
    
    /** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */
    void addAtIndex(int index, int val) {
        int listIndex=0;
        auto ptr=_head;
        while(ptr->next!=nullptr)
        {
            //找到了位置
            if(listIndex==index)
            {
                auto newNode=new SingleList();
                newNode->val=val;
                newNode->next=ptr->next;
                ptr->next=newNode;
                break;
            }
            else
            {
                ptr=ptr->next;
                listIndex++;
            }
                
        }
        if(ptr->next==nullptr&&listIndex==index)
        {
              auto newNode=new SingleList();
              newNode->val=val;
              newNode->next=ptr->next;
              ptr->next=newNode;
                
        }
    }
    
    /** Delete the index-th node in the linked list, if the index is valid. */
    void deleteAtIndex(int index) {
        int listIndex=0;
        auto ptr=_head;
        while(ptr->next!=nullptr)
        {
            //找到了位置
            if(listIndex==index)
            {
                auto delNode=ptr->next;
                //要删除的结点不是空
                if(delNode!=nullptr)
                {
                    ptr->next=delNode->next;
                    delete delNode;
                    break;
                }
                    
            }
            else
            {
                ptr=ptr->next;
                listIndex++;
            }
                
        }
    }
private:
    SingleList*  const _head;
};

/**
 * 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);
 */