Why Linked List Insertion Is O(1) Only Under a Hidden Assumption

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A developer writing on DEV Community shared a common misconception about linked list time complexity that took them a while to untangle. The confusion stemmed from the claim that linked list insertion is O(1), which is true only when you already hold a direct reference to the target node. If you must first search for that node by value, the traversal itself costs O(n), making the overall operation linear. The key distinction is that linked lists make structural rearrangement cheap, not the process of locating elements. The author concluded that many Big-O explanations are technically correct but omit the assumed preconditions that determine which operation is actually being measured.

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