THINK++ — Engineering Visualized

📖 LESSON

Frequency Counting

Frequency counting is a technique to record the number of occurrences of each element in a collection. It's used in problems involving duplicates, anagrams, and sets.

Frequency Array

Best for: Small integer ranges (e.g., 0-100 or 'a'-'z')

O(N) time, O(Range) space

Hash Map

Best for: Large or sparse ranges, non-integer keys

O(N) time, O(N) space

Frequency Counting

Simulation Lab v2.0

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Speed1000ms

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💡 The 'a' - 'z' Trick

For lowercase English letters, use an array of size 26. Access the frequency of character `c` using `arr[c - 'a']`. This is faster and uses less memory than a hash map.

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