Top K Frequent Elements

LeetCode 347 • Medium • Arrays & Hashing

Given nums and k, return the k most frequent elements. Bucket sort: index = frequency.

TimeO(n)count + bucket collect

SpaceO(n)count + buckets

Bucket i: — Result: —

Input / Count

Current bucket

Result

Count

—

Result

—

Speed:

Ready

Press Play. Count frequencies with a hash map, build buckets (index = freq), then collect from highest bucket down until we have k elements.

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Practice until you don't need to look. Use the guide comments below as scaffolding. The green highlights are the nuances to burn into memory.

# ─── TOP K FREQUENT (LeetCode 347) ───

# Pattern: Bucket sort — freq[i] = nums with count i

# Time: O(n) Space: O(n)

# 1. Define: topKFrequent(nums, k)

# 2. Count: count = Counter(nums)

# 3. Buckets: freq = [[] for _ in range(len(nums)+1)]

# for num, cnt in count.items(): freq[cnt].append(num)

# 4. Collect from high to low:

# res = []

# for i in range(len(freq)-1, 0, -1):

# for num in freq[i]: res.append(num); if len(res)==k: return res

# 5. Return: return res

# Vars: count, freq, res, i

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