Leetcode

Remove Linked List Elements

  • Time:O(n)
  • Space:O(1)

C++

class Solution {
 public:
  ListNode* removeElements(ListNode* head, int val) {
    ListNode dummy(0, head);
    ListNode* prev = &dummy;

    for (; head; head = head->next)
      if (head->val != val) {
        prev->next = head;
        prev = prev->next;
      }
    prev->next = nullptr;  // in case the last val == val

    return dummy.next;
  }
};

JAVA

class Solution {
  public ListNode removeElements(ListNode head, int val) {
    ListNode dummy = new ListNode(0, head);
    ListNode prev = dummy;

    for (; head != null; head = head.next)
      if (head.val != val) {
        prev.next = head;
        prev = prev.next;
      }
    prev.next = null; // in case the last val == val

    return dummy.next;
  }
}

Python

class Solution:
  def removeElements(self, head: ListNode, val: int) -> ListNode:
    dummy = ListNode(0, head)
    prev = dummy

    while head:
      if head.val != val:
        prev.next = head
        prev = prev.next
      head = head.next
    prev.next = None

    return dummy.next