DeleteNodeInALinkedList

Problem

https://leetcode.com/problems/delete-node-in-a-linked-list/

There is a singly-linked list head and we want to delete a node node in it.

You are given the node to be deleted node. You will not be given access to the first node of head.

All the values of the linked list are unique, and it is guaranteed that the given node node is not the last node in the linked list.

Delete the given node. Note that by deleting the node, we do not mean removing it from memory. We mean:

  • The value of the given node should not exist in the linked list.

  • The number of nodes in the linked list should decrease by one.

  • All the values before node should be in the same order.

  • All the values after node should be in the same order.

Custom testing:

  • For the input, you should provide the entire linked list head and the node to be given node. node should not be the last node of the list and should be an actual node in the list.

  • We will build the linked list and pass the node to your function.

  • The output will be the entire list after calling your function.

Example 1:

image1

Input: head = [4,5,1,9], node = 5
Output: [4,1,9]
Explanation: You are given the second node with value 5, the linked list should become 4 -> 1 -> 9 after calling your function.

Example 2:

image2

Input: head = [4,5,1,9], node = 1
Output: [4,5,9]
Explanation: You are given the third node with value 1, the linked list should become 4 -> 5 -> 9 after calling your function.

Constraints:

  • The number of the nodes in the given list is in the range [2, 1000].

  • -1000 <= Node.val <= 1000

  • The value of each node in the list is unique.

  • The node to be deleted is in the list and is not a tail node.

Solution

Because we do not have access to the previous node, we cannot delete node in the usual fashion by setting the previous node’s next pointer to node.next. Instead we can shift the values in the linked list to the left, dropping the tail node.

Pattern

Linked List

Code

from __future__ import annotations

from typing import List


class ListNode:
    """Node in a linked list.
    """

    def __init__(self, val: int, next: ListNode | None = None) -> None:
        self.val = val
        self.next = next

    def __str__(self) -> str:
        return str(self.val) + (' -> ' + str(self.next) if self.next is not None else '')

    @classmethod
    def from_list(cls, list: List[int]) -> ListNode | None:
        head: ListNode | None = None
        for el in list:
            if head is None:
                head = ListNode(el)
                node = head
            else:
                node.next = ListNode(el)
                node = node.next
        return head


def deleteNode(node: ListNode) -> None:
    """Delete ``node`` from a linked list.
    """
    while node is not None and node.next is not None:
        node.val = node.next.val
        if node.next.next is None:
            node.next = None

        node = node.next

Test

>>> from DeleteNodeInALinkedList import ListNode, deleteNode
>>> head = ListNode.from_list([4, 5, 1, 9])
>>> deleteNode(head.next)
>>> print(head)
4 -> 1 -> 9
>>> head = ListNode.from_list([4, 5, 1, 9])
>>> deleteNode(head.next.next)
>>> print(head)
4 -> 5 -> 9
class DeleteNodeInALinkedList.ListNode(val: int, next: ListNode | None = None)

Bases: object

Node in a linked list.

classmethod from_list(list: List[int]) → ListNode | None
DeleteNodeInALinkedList.deleteNode(node: ListNode) → None

Delete node from a linked list.