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Leetcode707:
Design your implementation of the linked list. You can choose to use a singly or doubly linked list.
A node in a singly linked list should have two attributes: val
and next
. val
is the value of the current node, and next
is a pointer/reference to the next node.
If you want to use the doubly linked list, you will need one more attribute prev
to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.
Implement the MyLinkedList
class:
MyLinkedList()
Initializes the MyLinkedList
object.int get(int index)
Get the value of the indexth
node in the linked list. If the index is invalid, return -1
.void addAtHead(int 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 addAtTail(int val)
Append a node of value val
as the last element of the linked list.void addAtIndex(int index, int val)
Add a node of value val
before the indexth
node in the linked list. If index
equals the length of the linked list, the node will be appended to the end of the linked list. If index
is greater than the length, the node will not be inserted.void deleteAtIndex(int index)
Delete the indexth
node in the linked list, if the index is valid.- 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
'运行
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