Remove Linked List Elements — LeetCode 203 Python Solution

The problem

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

Input

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

Output

[1,2,3,4,5]

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(-1, head)
        pre = dummy
        while pre.next:
            if pre.next.val != val:
                pre = pre.next
            else:
                pre.next = pre.next.next
        return dummy.next

Complexity

Pattern: Linked List

Rewire pointers in place, with a dummy head and a saved next to keep it safe. LeetCode 203. Remove Linked List Elements is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Linked List.

The linked list guide has the Python template for the pattern and the 75 LeetCode problems that use it.

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