代码随想录算法公开课day3

203. 移除链表元素 - 力扣（LeetCode）

本题要理解对象变换的操作，可变类型对象直接赋值后的变化对原对象的影响
引用自Python 直接赋值、浅拷贝和深度拷贝解析 | 菜鸟教程

1、b = a: 赋值引用，a 和 b 都指向同一个对象

2、b = a.copy(): 浅拷贝, a 和 b 是一个独立的对象，但他们的子对象还是指向统一对象（是引用）。

b = copy.deepcopy(a): 深度拷贝, a 和 b 完全拷贝了父对象及其子对象，两者是完全独立的。

# 法1 原链表删除元素
# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def removeElements(self, head: Optional[ListNode], val: int) -> Optional[ListNode]:
        while head != None and head.val == val:
            head = head.next
        current = head
        while current != None and current.next != None:
            if current.next.val == val:
                current.next = current.next.next
            else:
                current = current.next
        return head

        

# 法2 虚拟头节点
# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def removeElements(self, head: Optional[ListNode], val: int) -> Optional[ListNode]:
        new = ListNode(None,head)
        current = new
        while current != None and current.next != None:
            if current.next.val == val:
                current.next = current.next.next
            else:
                current = current.next
        new = new.next
        return new

707. 设计链表 - 力扣（LeetCode）

# 法1 单链表
class ListNode:
    def __init__(self,val = 0,next = None):
        self.val = val
        self.next = next

class MyLinkedList:

    def __init__(self):
        self.fake_head = ListNode()
        self.size = 0

    def get(self, index: int) -> int:
        if index < 0 or index > self.size - 1:
            return -1
        result = self.fake_head.next
        for i in range(index):
            result = result.next
        return result.val

    def addAtHead(self, val: int) -> None:
        add_ = ListNode(val,self.fake_head.next)
        self.fake_head.next = add_
        self.size += 1

    def addAtTail(self, val: int) -> None:
        result = self.fake_head
        while result.next != None:
            result = result.next
        result.next = ListNode(val)
        self.size += 1

    def addAtIndex(self, index: int, val: int) -> None:
        if index > self.size:
            pass
        elif index == self.size:
            self.addAtTail(val)
        else:
            result = self.fake_head
            for i in range(index):
                result = result.next
            result.next = ListNode(val,result.next) 
            self.size += 1      
        
    def deleteAtIndex(self, index: int) -> None:
        if index < 0 or index > self.size - 1:
            pass
        else:
            result = self.fake_head
            for i in range(index):
                result = result.next
            result.next = result.next.next
            self.size -= 1
        
# Your MyLinkedList object will be instantiated and called as such:
# obj = MyLinkedList()
# param_1 = obj.get(index)
# obj.addAtHead(val)
# obj.addAtTail(val)
# obj.addAtIndex(index,val)
# obj.deleteAtIndex(index)

复习

203. 移除链表元素 - 力扣（LeetCode）

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def removeElements(self, head: Optional[ListNode], val: int) -> Optional[ListNode]:
        v = ListNode(0,head)
        current = v
        while current.next:
            if current.next.val == val:
                current.next = current.next.next
            else:
                current = current.next
        return v.next

707. 设计链表 - 力扣（LeetCode）

class ListNode:
    def __init__(self,val = 0,next = None):
        self.val = val
        self.next = next
class MyLinkedList:

    def __init__(self):
        self.head = ListNode()
        self.size = 0

    def get(self, index: int) -> int:
        if index >= self.size:
            return -1
        current = self.head.next
        for i in range(index):
            current = current.next
        return current.val

    def addAtHead(self, val: int) -> None:
        new = ListNode(val,self.head.next)
        self.head.next = new
        self.size += 1

    def addAtTail(self, val: int) -> None:
        current = self.head
        for i in range(self.size):
            current = current.next
        current.next = ListNode(val)
        self.size += 1
        
    def addAtIndex(self, index: int, val: int) -> None:
        if index < 0 or index > self.size:
            pass
        else:
            current = self.head
            for i in range(index):
                current = current.next
            new = ListNode(val,current.next)
            current.next = new
            self.size += 1

    def deleteAtIndex(self, index: int) -> None:
        if index < 0 or index >= self.size:
            pass
        else:
            current = self.head
            for i in range(index):
                current = current.next
            current.next = current.next.next
            self.size -= 1 
        


# Your MyLinkedList object will be instantiated and called as such:
# obj = MyLinkedList()
# param_1 = obj.get(index)
# obj.addAtHead(val)
# obj.addAtTail(val)
# obj.addAtIndex(index,val)
# obj.deleteAtIndex(index)