LeetCode/83. RemoveDuplicatesFromSortedList

Summary

Solutions

My Solution

When I was solving this problem I made mistakes at start.

  1. I didn’t think about it is SortedLists. Which make me use HashSet.

Also I was confused using pointer properly. Was thinking too much ended up using 3 pointers.

public ListNode Solution(ListNode head)
{
    var output = new ListNode(0);
    var resultNode = output;
    var outputTail = head;
    var dict = new HashSet<int>();

    while (outputTail != null)
    {
        if (dict.Add(outputTail.val))
        {
            var node = new ListNode(outputTail.val);
            output.next = node;
            output = output.next;
        }
        outputTail = outputTail.next;
    }

    return resultNode.next;
}

Best Solution

The best solution was simpler than I thought. It only use one pointer. Also looping list.next rather than list node itself.
By keep assigning ref, list = list.next & list.next = list.next.next, I will change head node itself.
Really need to think about pointer.

public ListNode BestSolution(ListNode head)
{
    if (head == null || head.next == null) return head;

    ListNode list = head;

    while (list.next != null)
    {
        if (list.val == list.next.val) list.next = list.next.next;
        else list = list.next;
    }

    return head;
}
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