203. Remove Linked List Elements

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

Remove all elements from a linked list of integers that have value val.

Example:

Input:  1->2->6->3->4->5->6, val = 6
Output: 1->2->3->4->5

--
Intuition
Have a prev pointer
If head.val == target
   Set the prev to head.next
else
   prev = prev.next

Preprocess
Corner case, while head.val == target at the beginning of list
--
Related problems
237-delete-node-in-linked-list
---

	/**
	* Definition for singly-linked list.
	* public class ListNode {
	* int val;
	* ListNode next;
	* ListNode() {}
	* ListNode(int val) { this.val = val; }
	* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
	* }
	*/
	class Solution {
	public ListNode removeElements(ListNode head, int val) {
	while (head != null && head.val == val) {
	head = head.next;
	}
	ListNode ans = head;
	while (head != null && head.next != null) {
	if (head.next.val == val) {
	head.next = head.next.next;
	} else {
	head = head.next;
	}
	}
	return ans;
	}
	}

view raw 203.RemoveLinkedListElements.java hosted with ❤ by GitHub

	/**
	* Definition for singly-linked list.
	* public class ListNode {
	* int val;
	* ListNode next;
	* ListNode() {}
	* ListNode(int val) { this.val = val; }
	* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
	* }
	*/
	class Solution {
	public ListNode removeElements(ListNode head, int val) {
	ListNode prev = new ListNode(-1), current = head;
	prev.next = head;
	ListNode ans = prev;
	while (current != null) {
	if (current.val == val) {
	prev.next = current.next;
	} else {
	prev = prev.next;
	}
	current = current.next;
	}
	return ans.next;
	}
	}

view raw 203.RemoveLinkedListElements.java hosted with ❤ by GitHub

	# 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:
	prev = ListNode(-1)
	prev.next = head
	current = head
	ans = prev
	while current:
	if current.val == val:
	prev.next = current.next
	else:
	prev = prev.next
	current = current.next
	return ans.next

view raw 203.RemoveLinkedListElements.py hosted with ❤ by GitHub