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Remove Duplicates from Sorted List II

Problem statement​

Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well.

Example 1:

Input: head = [1,2,3,3,4,4,5]Output: [1,2,5]

Example 2:

Input: head = [1,1,1,2,3]Output: [2,3]

Constraints:

  • The number of nodes in the list is in the range [0, 300].
  • -100 <= Node.val <= 100
  • The list is guaranteed to be sorted in ascending order.

My solution​

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var deleteDuplicates = function(head) {
    if (!head || !head.next) {
        return head;
    }
    
    const dummy = new ListNode(null, head);
    let prev = dummy;
    let node = head;
    
    while(node?.next) {
        if (node.val === node.next.val) {
        // console.log(node)
            while (node.next && node.val === node.next.val) {
                node = node.next
            }
            node = node.next;
            prev.next = node;
        
        } else {
            prev = node;
            node = node.next;
        }
    }
    
    return dummy.next;
};