Typorithm · easy

Frequency Counter Intro

patternsfrequency-counterlookup

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Full lesson · 3 learning steps Open any exercise for focused practice

Step 1 of 3 · intro card

Learn Frequency Counter

Basic Patterns

A frequency counter stores how many times each value appears.

Instead of comparing every value with every other value, a counter records counts in an object or Map.

Each input value becomes a key, and the stored number grows as the value appears again.

This pattern often turns repeated searching into direct lookup.

Create a counter object.

Loop through the input once.

Use the current item as the lookup key.

Increase the stored count by one.

function countValues(items) {
  const counts = {};

  for (const item of items) {
    counts[item] = (counts[item] ?? 0) + 1;
  }

  return counts;
}

Read the concept map and follow the code breakdown.

Type the implementation, repair mistakes and work through every recall exercise.

Use the final check without hints; revisit weak concepts in short practice sessions.