<p>Given the <code>head</code> of a sorted linked list, <em>delete all duplicates such that each element appears only once</em>. Return <em>the linked list <strong>sorted</strong> as well</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/04/list1.jpg" style="width: 302px; height: 242px;" />
<pre>
<strong>Input:</strong> head = [1,1,2]
<strong>Output:</strong> [1,2]
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/04/list2.jpg" style="width: 542px; height: 222px;" />
<pre>
<strong>Input:</strong> head = [1,1,2,3,3]
<strong>Output:</strong> [1,2,3]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the list is in the range <code>[0, 300]</code>.</li>
	<li><code>-100 &lt;= Node.val &lt;= 100</code></li>
	<li>The list is guaranteed to be <strong>sorted</strong> in ascending order.</li>
</ul>

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if (!head || !head->next) {
            return head;
        }

        ListNode* current = head;

        while (current && current->next) {
            if (current->val == current->next->val) {
                ListNode* duplicate = current->next;
                current->next = duplicate->next;
                delete duplicate;
            }
            else {
                current = current->next;
            }
        }
        return head;
    }
};
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