Algo.LinkedLists.DeleteNode

way 1, with sentinent or nullNode approach, shrinks partial cases

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution {
    public ListNode RemoveElements(ListNode head, int val) {
        if (head == null)
            return null;
        
        ListNode nullNode = new ListNode();
        nullNode.next = head;
        ListNode current = nullNode;
        
        // start node and middle
        while (current.next.next != null) {
          
            if (current.next.val == val) {
                current.next = current.next.next;
                continue;
            }
            
            current = current.next;
        }
        
        // last node
        if (current.next.val == val)
            current.next = null;
        
        return nullNode.next;
    }
}

way2, more partial cases

public ListNode RemoveElements(ListNode head, int val)
            {
                if (head == null)
                    return null;

                ListNode res = head;

                ListNode current = head;
                ListNode previous = null;
                bool wasDeletedFromMiddle = false;

                while (current != null)
                {
                    if (current.val == val)
                    {
                        // head
						if (current == head)
                        {
                            head = head.next;
                            res = head;
                        }
                        // body
						else if (current != head && current.next != null)
                        {
                            if (current.next != null && current.next.val == val)
                            {
                                current = current.next;
                                continue;
                            }

                            previous.next = current.next;
                        }
                        // tail
                        else if (current != head && current.next == null)
                        {
                            previous.next = null;
                        }
                    }
                    
                    previous = current;
                    current = current.next;
                }

                return res;
            }
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