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Remove Linked List Elements

Problem Statement​

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:​

alt text

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 <= val <= 50

Leetcode Link

Code​

Python
class Solution:
    def removeElements(self, head: Optional[ListNode], val: int) -> Optional[ListNode]:
        temp = head
        prev = None             # initially prev should points to None
        while temp!=None:
            if temp.val == val and prev == None :      # when first node is val which has to remove
                temp = temp.next
                head = temp
                prev = None                         # prev must None because still first Node equal to val
            elif temp.val == val:               # when in middle node equal to val
                prev.next = temp.next               # simple prev point to next node
                temp = temp.next
            else:                               # Move untill node not equal to val
                prev = temp
                temp = temp.next
        return head