What is the time and space complexity of Get All DOM Tags?

Time complexity: O(n) where n is the number of nodes. Space complexity: O(u) where u is the number of unique tags.

Get All DOM Tags

Easy

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Solution Guide: Get All DOM Tags

Approach

Traverse the tree recursively, adding each node's tag name (lowercased) to a Set to collect unique values. Sort the Set into an array for the final result. Extend with a counting variant that uses an object to tally occurrences of each tag.

Complexity Analysis

Time: O(n) where n is the number of nodes
Space: O(u) where u is the number of unique tags

Pattern

Tree Traversal Collection

Why It Works

A Set automatically deduplicates tag names during traversal, and lowercasing before insertion ensures case-insensitive uniqueness across mixed-case DOM trees.

Updated Feb 2026