0707-leetcode算法实现之设计链表-design-linked-list-python&golang实现

设计链表的实现。您可以选择使用单链表或双链表。单链表中的节点应该具有两个属性：val 和 next。val 是当前节点的值，next 是指向下一个节点的指针/引用。如果要使用双向链表，则还需要一个属性 prev 以指示链表中的上一个节点。假设链表中的所有节点都是 0-index 的。

在链表类中实现这些功能：

get(index)：获取链表中第 index 个节点的值。如果索引无效，则返回-1。
addAtHead(val)：在链表的第一个元素之前添加一个值为 val 的节点。插入后，新节点将成为链表的第一个节点。
addAtTail(val)：将值为 val 的节点追加到链表的最后一个元素。
addAtIndex(index,val)：在链表中的第 index 个节点之前添加值为 val  的节点。如果 index 等于链表的长度，则该节点将附加到链表的末尾。如果 index 大于链表长度，则不会插入节点。如果index小于0，则在头部插入节点。
deleteAtIndex(index)：如果索引 index 有效，则删除链表中的第 index 个节点。

示例：

MyLinkedList linkedList = new MyLinkedList();
linkedList.addAtHead(1);
linkedList.addAtTail(3);
linkedList.addAtIndex(1,2); //链表变为1-> 2-> 3
linkedList.get(1); //返回2
linkedList.deleteAtIndex(1); //现在链表是1-> 3
linkedList.get(1); //返回3

提示：

所有val值都在 [1, 1000] 之内。
操作次数将在  [1, 1000] 之内。
请不要使用内置的 LinkedList 库。

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/design-linked-list

python

# 0707.设计链表实现以下5中功能：
# -根据索引获取值
# -头插
# -尾插
# -根据索引插入
# -根据索引删除

# 单链表
class Node:
    def __init__(self, val):
        self.val = val
        self.next = None

class Mylinklist:
    def __init__(self, node=None):
        if node != None:
            # 当节点非空时，实例化节点，让头结点指向节点
            headNode = Node(node)
            self._head = headNode
        else:
            # 如果节点空，头结点指向None
            self._head = node

    def length(self):
        """
        初始化计数，当节点非空，不断右移，计数器++，重复，返回计数
        :return:
        """
        cnt = 0
        cur = self._head
        while cur:
            cur = cur.next
            cnt += 1
        return cnt

    def transverse(self):
        """
        当前节点即为头结点，非空即打印节点值，指针右移，重复
        :return:
        """
        cur = self._head
        while cur:
            print(cur.val)
            cur = cur.next

    def get(self, index: int) -> int:
        """
        初始化计数器，初始化从头结点开始，遍历节点，
        如果遍历到计数器等于index，即找到合适index的值返回，
        否则计数器++，链表指针右移，重复
        如果遍历链表没有index，即返回-1，表示index超出了链表范围
        :param index:
        :return:
        """
        cnt = 0
        cur =self._head
        while cur:
            if cnt == index:
                return cur.val
            cnt += 1
            cur = cur.next
        return -1

    def addAtHead(self, val) -> None:
        """
        头部插入节点，根据节点值，生成节点对象，让该节点指向头结点，头结点指向node
        :param val:
        :return:
        """
        node = Node(val)
        node.next = self._head # 代表节点指向头结点的next对象
        self._head = node

    def addAtTail(self, val: int) -> None:
        node = Node(val)
        # 尾部插入判断当前链表是否空
        # 空链表时，头部指向为空，直接让头部指向节点
        if self._head == None:
            self._head = Node
        # 一般情况下，遍历到尾部，尾部节点指向插入节点，插入节点指向None
        else:
            cur = self._head
            # 遍历到最后一个节点时，next为None，即break循环
            while cur.next != None:
                cur = cur.next
            # 尾部节点指向插入节点，完成尾部插入
            cur.next = node

    def addAtIndex(self, index: int, val: int) -> None:
        """
        给定插入位置，与插入的值，需要插入位置的前序节点pre, 和当前节点cur，
        pre指向node, node指向cur
        :param val:
        :return:
        """
        node = Node(val)
        # index < 0，头插
        if index < 0:
            self.addAtHead(val)
        # index越界，尾插
        elif index > self.length():
            self.addAtTail(val)
        # 一般情况，链表中插入
        # 通过遍历计数比较index获取index-1位置节点
        # 插入节点的next指针指向p先序节点的next
        # 先序节点指向插入节点，完成插入，且不断
        else:
            cnt = 0
            pre = self._head
            while cnt < index:
                pre = pre.next
                cnt += 1
            node.next = pre.next
            pre.next = node

    def deleteAtIndex(self, index: int) -> None:
        # 给定index<0，直接返回空
        if index < 0:
            return
        # index为0时，头部指向当前头部的next即可
        elif index == 0:
            self._head = self._head.next
        # 一般情况下index>0, 分链表长度内的或越界的，2种情况
        else:
            cnt = 0
            cur = self._head
            while cnt < index:
                cur = cur.next
                cnt += 1
            # 遍历结束后，index-1位置的元素的next指向其next的next
            if cur.next != None:
                cur.next = cur.next.next
            # 否则，越界
            else:
                return




if __name__ == "__main__":
    node = Mylinklist()
    node.addAtHead(200)
    print(node.get(0))
    node.addAtHead(250)
    node.addAtTail(260)
    node.addAtIndex(2,251)
    print(node.get(0))
    node.transverse()
    print(node.length())
    node.deleteAtIndex(1)
    print(node.length())
    node.transverse()
---以下为官方
class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None

class MyLinkedList:
    def __init__(self):
        self.size = 0
        self.head = ListNode(0)  # sentinel node as pseudo-head
        

    def get(self, index: int) -> int:
        """
        Get the value of the index-th node in the linked list. If the index is invalid, return -1.
        """
        # if index is invalid
        if index < 0 or index >= self.size:
            return -1
        
        curr = self.head
        # index steps needed 
        # to move from sentinel node to wanted index
        for _ in range(index + 1):
            curr = curr.next
        return curr.val
            

    def addAtHead(self, val: int) -> None:
        """
        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.
        """
        self.addAtIndex(0, val)
        

    def addAtTail(self, val: int) -> None:
        """
        Append a node of value val to the last element of the linked list.
        """
        self.addAtIndex(self.size, val)
        

    def addAtIndex(self, index: int, val: int) -> None:
        """
        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.
        """
        # If index is greater than the length, 
        # the node will not be inserted.
        if index > self.size:
            return
        
        # [so weird] If index is negative, 
        # the node will be inserted at the head of the list.
        if index < 0:
            index = 0
        
        self.size += 1
        # find predecessor of the node to be added
        pred = self.head
        for _ in range(index):
            pred = pred.next
            
        # node to be added
        to_add = ListNode(val)
        # insertion itself
        to_add.next = pred.next
        pred.next = to_add
        

    def deleteAtIndex(self, index: int) -> None:
        """
        Delete the index-th node in the linked list, if the index is valid.
        """
        # if the index is invalid, do nothing
        if index < 0 or index >= self.size:
            return
        
        self.size -= 1
        # find predecessor of the node to be deleted
        pred = self.head
        for _ in range(index):
            pred = pred.next
            
        # delete pred.next 
        pred.next = pred.next.next
---双向链表
# 双向链表
class ListNode:
    def __init__(self, val):
        self.val = val
        self.next, self.prev = None, None


class MyLinkerList:
    def __init__(self):
        self.size = 0
        # 哨兵作为虚拟头尾节点
        self.head, self.tail = ListNode(0), ListNode(0)
        self.head.next = self.tail
        self.tail.prev = self.head

    def get(self, index: int) -> int:
        if index < 0 or index >= self.size:
            return -1
        # 头部遍历
        if index + 1 < self.size - index:
            cur = self.head
            for _ in range(index+1):
                cur = cur.next
        # 尾部遍历
        else:
            cur = self.tail
            for _ in range(self.size - index):
                cur = cur.prev
        return cur.val

    def addAtHead(self, val: int) -> None:
        prev, next = self.head, self.head.next # 头部前2节点
        self.size += 1 # 新增加点，长度加1
        node = ListNode(val)
        node.prev = prev # 插入节点前序指针指向头1节点
        node.next = next # 插入节点后继指针指向原头二节点
        prev.next = node # 头1节点后继指针指向节点
        next.prev = node # 原头2节点的前序指针指向节点

    def addAtTail(self, val: int) -> None:
        # 与头插类似
        next, prev = self.tail, self.tail.prev
        self.size += 1
        node = ListNode(val)
        node.prev = prev
        node.next = next
        prev.next = node
        next.prev = node

    def addAtIndex(self, index: int, val: int) -> None:
        if index > self.size:
            return
        if index < 0:
            index = 0
        if index < self.size - index: # 头部插入，向后遍历
            prev = self.head
            for _ in range(index):
                prev = prev.next
            next = prev.next
        else: # 尾部插入，向前遍历
            next = self.tail
            for _ in range(self.size-index):
                next = next.prev
            prev = next.prev
        self.size += 1
        node = ListNode(val)
        node.prev = prev
        node.next = next
        prev.next = node
        next.prev = node

    def deleteAtIndex(self, index: int) -> None:
        if index < 0 or index > index.size:
            return

        if index < self.size - index:
            prev = self.head
            for _ in range(index):
                prev = prev.next
            next = prev.next.next
        else:
            next = self.tail
            for _ in range(self.size-index):
                next = next.prev
            prev = next.prev.prev

        # rm node
        self.size -= 1
        prev.next = next
        next.prev = prev

golang

# 单链表
type ListNode struct {
	Val  int
	Next *ListNode
}

type MyLinkedList struct {
	size int
	head *ListNode
}

// initialize data structure
func Constructor() MyLinkedList {
	return MyLinkedList{
		0,
		&ListNode{},
	}
}

func (this *MyLinkedList) Get(index int) int {
	if index < 0 || index > this.size {
		return -1
	}
	prev := this.head
	for i := 0; i < index; i++ {
		prev = prev.Next
	}
	return prev.Next.Val
}

func (this *MyLinkedList) AddAtHead(val int) {
	this.AddAtIndex(0, val)
}

func (this *MyLinkedList) AddAtTail(val int) {
	this.AddAtIndex(this.size, val)
}

func (this *MyLinkedList) AddAtIndex(index int, val int) {
	if index < 0 || index > this.size {
		return
	}
	pre := this.head
	for i := 0; i < index; i++ {
		pre = pre.Next
	}
	node := &ListNode{Val: val}
	node.Next = pre.Next
	pre.Next = node
	this.size++
}

func (this *MyLinkedList) DeleteAtIndex(index int) {
	if index < 0 || index > this.size {
		return
	}
	prev := this.head
	for i := 0; i < index; i++ {
		prev = prev.Next
	}
	prev.Next = prev.Next.Next
	this.size++
}
---以下双链表

// 定义链表节点
type Node struct {
	Next *Node
	Prev *Node
	Val  int
}

type MyLinkedList struct {
	head *Node // 头结点
	tail *Node // 尾结点
	size int   // 链表的长度
}

/** Initialize your data structure here. */
func Constructor() MyLinkedList {
	return MyLinkedList{}
}

/** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
func (this *MyLinkedList) Get(index int) int {
	// index无效
	if this.size == 0 || index < 0 || index >= this.size {
		return -1
	}
	// index为头尾节点
	if index == 0 {
		return this.head.Val
	}
	if index == this.size-1 {
		return this.tail.Val
	}
	// 下面选择更快的遍历方向, 查看index在偏头部还是偏尾部
	cur := this.head
	count := 0
	for cur != nil {
		if count == index {
			break
		}
		count++
		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. */
func (this *MyLinkedList) AddAtHead(val int) {
	node := &Node{Val: val}
	
	if this.head != nil {
		node.Next = this.head
		this.head.Prev = node
		this.head = node
	} else {
		this.head = node
		this.tail = this.head
	}
	this.size++
}

/** Append a node of value val to the last element of the linked list. */
func (this *MyLinkedList) AddAtTail(val int) {
	node := &Node{Val: val}
	
	if this.tail != nil {
		node.Prev = this.tail
		this.tail.Next = node
		this.tail = node
	} else {
		this.tail = node
		this.head = this.tail
	}
    this.size++
	
}

/** 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. */
func (this *MyLinkedList) AddAtIndex(index int, val int) {
	if index > this.size {
		return
	}
	if index <= 0 {
		this.AddAtHead(val)
		return
	}
	if index == this.size {
		this.AddAtTail(val)
		return
	}
	cur := this.head
	count := 0
	for cur != nil && count < index {
		count++
		cur = cur.Next
	}
	// 在当前节点cur的前面插入
	this.size++
	node := &Node{Val: val, Next: cur, Prev: cur.Prev}
	cur.Prev.Next = node
	cur.Prev = node
}

/** Delete the index-th node in the linked list, if the index is valid. */
func (this *MyLinkedList) DeleteAtIndex(index int) {
	// 如果索引无效 || 链表为空
	if this.size == 0 || index < 0 || index >= this.size {
		return
	}
	if index == 0 {
		// 如果删除的是头结点
		this.head = this.head.Next
	} else if index == this.size-1 {
		// 如果删除的是尾结点
		this.tail = this.tail.Prev
	} else {
		cur := this.head
		count := 0
		for cur != nil && count < index {
			count++
			cur = cur.Next
		}
		// 找到要删除的节点cur了
		cur.Next.Prev = cur.Prev
		cur.Prev.Next = cur.Next
	}
	this.size--
}