Sorted List, Unique Values Only

Medium

You get a singly linked list starting at head, sorted in non-decreasing order. If a value occurs more than once, delete **all** nodes holding it, without keeping a single copy. Return the head of the resulting list; it stays sorted. The list may be empty.

Example 1

head=list_node([-3, 0, 0, 2, 7, 7, 7, 9]) → [-3, 2, 9]

The values 0 and 7 repeat, so all their nodes are removed. What remains is -3 → 2 → 9.

Example 2

head=list_node([4, 4]) → None

The only value repeats, so the list becomes empty.

Example 3

head=list_node([1, 5, 6]) → [1, 5, 6]

Constraints

0 ≤ number of nodes ≤ 300
-100 ≤ Node.val ≤ 100
The list is sorted in non-decreasing order

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Topics

Linked List Two Pointers

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Input

head=list_node([-3, 0, 0, 2, 7, 7, 7, 9])

Expected

[-3, 2, 9]

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