Top K Frequent Elements

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Problem

Given an integer array nums and an integer k, return the k most frequently occurring elements in the array, in any order.

Examples

Example 1

Input:nums = [1,1,1,2,2,3], k = 2

Output:[1,2]

Example 2

Input:nums = [1], k = 1

Output:[1]

Constraints

The answer is guaranteed to be unique.
1 <= k <= number of distinct elements in nums.

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How to approach it: the Arrays & Hashing pattern

Arrays give O(1) index access; hash maps and sets give O(1) average lookup, insert, and delete by trading space for speed. Together they're the toolkit for turning brute-force O(n²) comparisons into a single O(n) pass.

Look for this pattern when

You need to check "have I seen this value before?" quickly.
You're counting occurrences or grouping items by a derived key (e.g. sorted letters for anagrams).
A nested loop is comparing every pair — a hash map can often replace the inner loop.

Read the full Arrays & Hashing guide →

Video walkthroughs

Original problem on LeetCode ↗