代码随想录一刷——707.设计链表

使用虚拟节点法进行链表的设计

1.在操作过程中一定要注意边界条件，否则代码通过不了，比如对链表尾部进行操作的时候

2.注意在内存的申请

编程实现

C++：

class MyLinkedList {

public:

    //定义链表结构体

    struct LinkNode

    {

        int val;

        LinkNode* next;

        LinkNode(int val):val(val), next(nullptr){}

    };

    //构造函数

    MyLinkedList()

    {

        size = 0;

        dummyHead = new LinkNode(0);

    }

   

    //获取链表中下标为index的节点的值

    int get(int index)

    {

        if(index > (size - 1) || index < 0)

            return -1;

        LinkNode* cur = dummyHead->next;

        while(index--)

        {

            cur = cur->next;

        }

        return cur->val;

    }

   

    //将一个值为val的节点插入到链表中的第一个元素之前

    void addAtHead(int val)

    {

        LinkNode* newnode = new LinkNode(val);

        newnode->next = dummyHead->next;

        dummyHead->next = newnode;

        size++;

    }

   

    //将一个值为val的节点追加到链表中作为链表的最后一个元素

    void addAtTail(int val)

    {

        LinkNode* newnode = new LinkNode(val);

        LinkNode* cur = dummyHead;

        while(cur->next != nullptr)

        {

            cur = cur->next;

        }

        cur->next = newnode;

        //newnode->next = nullptr;

        size++;

    }

   

    //将一个值为val的节点插入到链表中下标为index的节点之前。

    void addAtIndex(int index, int val)

    {

        if(index > size) return;

        if(index < 0) index = 0;

        LinkNode* newnode = new LinkNode(val);

        LinkNode* cur = dummyHead;

        while(index--)

        {

            cur = cur->next;

        }

        newnode->next = cur->next;

        cur->next = newnode;

        size++;

    }

   

    void deleteAtIndex(int index)

    {

        if(index > (size - 1) || index < 0) return;

        LinkNode* cur = dummyHead;

        while(index--)

        {

            cur = cur->next;

        }

        LinkNode* tmp = cur->next;

        cur->next = cur->next->next;

        delete tmp;

        tmp = nullptr;

        size--;

    }

    //打印链表

    void printLink()

    {

        LinkNode* cur = dummyHead;

        while(cur->next != nullptr)

        {

            cout << cur->next->val << " ";

            cur = cur->next;

        }

        cout << endl;

    }

private:

    int size;

    LinkNode* dummyHead;

};

C：

typedef struct Node {

    int val;

    struct Node* next;

} Node;

 

typedef struct {

    int size;

    Node* data;

} MyLinkedList;

/** Initialize your data structure here. */

MyLinkedList* myLinkedListCreate() {

    MyLinkedList* obj = (MyLinkedList*)malloc(sizeof(MyLinkedList));

    Node* head = (Node*)malloc(sizeof(Node));

    head->next = NULL;

    obj->data = head;

    obj->size = 0;

    return obj;

}

/** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */

int myLinkedListGet(MyLinkedList* obj, int index) {

    if (index < 0 || index >= obj->size) return -1;

    Node* cur = obj->data->next;

    while (index--) {

        cur = cur->next;

    }

    return cur->val;

}

/** 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 myLinkedListAddAtHead(MyLinkedList* obj, int val) {

    Node* node = (Node*)malloc(sizeof(Node));

    node->val = val;

    Node* cur = obj->data;

    node->next = cur->next;

    cur->next = node;

    obj->size++;

}

void myLinkedListAddAtTail(MyLinkedList* obj, int val)

{

    Node* node = (Node*)malloc(sizeof(Node));

    node->val = val;

    Node* cur = obj->data;

    while(cur->next != NULL)

    {

        cur = cur->next;

    }

    cur->next = node;

    node->next = NULL;

    obj->size++;

}

void myLinkedListAddAtIndex(MyLinkedList* obj, int index, int val)

{

    Node* node = (Node*)malloc(sizeof(Node));

    node->val = val;

    Node* cur = obj->data;

    if(index < 0 || index > obj->size) return;

    else if(index == obj->size) //这种情况是插入到链表的尾端

    {

       

        while(cur->next != NULL)

        {

            cur = cur->next;

        }

        cur->next = node;

        node->next = NULL;

        obj->size++;

    }

    else

    {

        while (index--) {

            cur = cur->next;

        }

        node->next = cur->next;

        cur->next = node;

        obj->size++;

    }

}

void myLinkedListDeleteAtIndex(MyLinkedList* obj, int index) {

    if(index < 0 || index >= obj->size) return;

    Node* cur = obj->data;

    while(index--)

    {

        cur = cur->next;

    }

    Node* tmp = cur->next;

    cur->next = cur->next->next;

    free(tmp);

    obj->size--;

}

void myLinkedListFree(MyLinkedList* obj) {

    Node* tmp = obj->data;

    while(tmp != NULL)

    {

        Node* n = tmp;

        tmp = tmp->next;

        free(n);

    }

    free(obj);

}

Python：

class LinkNode:

    def __init__(self,val = 0,next = None):

        self.val = val

        self.next = next

class MyLinkedList(object):

    def __init__(self):

        self.dummyHead = LinkNode()

        self.size = 0

    def get(self, index):

        """

        :type index: int

        :rtype: int

        """

        if index < 0 or index >= self.size:

            return -1

        cur = self.dummyHead.next

        for i in range(index):

            cur = cur.next

        return cur.val

       

    def addAtHead(self, val):

        """

        :type val: int

        :rtype: None

        """

        self.dummyHead.next = LinkNode(val,self.dummyHead.next)

        self.size += 1

    def addAtTail(self, val):

        """

        :type val: int

        :rtype: None

        """

        cur = self.dummyHead

        while cur.next:

            cur = cur.next

        cur.next = LinkNode(val)

        self.size += 1

    def addAtIndex(self, index, val):

        """

        :type index: int

        :type val: int

        :rtype: None

        """

        cur = self.dummyHead

        if index < 0 or index > self.size:

            return

        elif index == self.size:

            while cur.next:

                cur = cur.next

            cur.next = LinkNode(val)

        elif index < self.size:

            for i in range(index):

                cur = cur.next

            cur.next = LinkNode(val,cur.next)

        self.size += 1

       

    def deleteAtIndex(self, index):

        """

        :type index: int

        :rtype: None

        """

        if index < 0 or index >= self.size:

            return

        cur = self.dummyHead

        for i in range(index):

            cur = cur.next

        cur.next = cur.next.next

        self.size -= 1

   

    def printLink(self):

        cur = self.dummyHead

        while cur.next:

            print(cur.val)

注意在插入或者删除结点的操作时，n所指向的都是cur->next，我们需要得到的是n-1所对应的也即是cur，这样进行插入删除操作才不会出错。