#83.Remove Duplicates from Sorted List

Problem statement

Given the head of a sorted linked list, delete all duplicates such that each element appears only once. Return the linked list sorted as well.

Example 1

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

Example 2

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

Explanation

給定一個從頭開始的已排序鏈結串列，刪除串列裡重複的元素，使每個元素只出現一次，最終返回一個排序好的鏈結串列

Solution

熟悉鏈結串列的話這題不難，刪除重複值的方法是略過下個節點，將節點與下下個節點連接起來，特別注意的地方是要如何知道該節點是重複值，用變數紀錄嗎？還是有其他方法？

我從題目知道該串列是已經排序過，故將當前的節點值與下一個節點值比對是否相同，如果相同就用前面提到的刪除方式，略過下一個節點，將當前節點與下下節點連結起來；若不相同則將指標位置移動到下一個節點，重複以上步驟直到下一個節點指標為 null 為止

public ListNode DeleteDuplicates(ListNode head)
{
    if (head != null)
    {
        var curr = head;

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

    return head;
}

Reference

LeetCode Solution

GitHub Repository

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