LeetCode 203. Remove Linked List Elements

Description

https://leetcode.com/problems/remove-linked-list-elements/

Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head.

Example 1:

Input: head = [1,2,6,3,4,5,6], val = 6
Output: [1,2,3,4,5]

Example 2:

Input: head = [], val = 1
Output: []

Example 3:

Input: head = [7,7,7,7], val = 7
Output: []

Constraints:

• The number of nodes in the list is in the range [0, 104].
• 1 <= Node.val <= 50
• 0 <= k <= 50

Explanation

Iterate the linked list and have a previous variable to track the previous node. If the node value equals to the value, link the previous node to the next node.

Python Solution

# 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: ListNode, val: int) -> ListNode:
        dummy = ListNode(0)
        
        dummy.next = head
        
        prev = dummy
        
        while head != None:
            if head.val == val:
                prev.next = head.next
            else:
                prev = head            
            head = head.next
            
        return dummy.next