Count Words with Given Prefix in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a word starts with the given prefix.

DSA Typescript

function startsWith(word: string, prefix: string): boolean {
  return word.[1](prefix);
}

Drag options to blanks, or click blank then click option'

AindexOf

Bincludes

CendsWith

DstartsWith

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'includes' checks anywhere in the string, not just the start.

The startsWith method checks if the string begins with the given prefix.

2fill in blank

medium

Complete the code to count how many words start with the prefix.

DSA Typescript

function countWords(words: string[], prefix: string): number {
  let count = 0;
  for (const word of words) {
    if (word.[1](prefix)) {
      count++;
    }
  }
  return count;
}

Drag options to blanks, or click blank then click option'

Aincludes

BstartsWith

CendsWith

DindexOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'includes' counts words that have the prefix anywhere, not just at the start.

We use startsWith to check if each word begins with the prefix and count those that do.

3fill in blank

hard

Fix the error in the function to return the correct count of words starting with prefix.

DSA Typescript

function countWords(words: string[], prefix: string): number {
  let count = 0;
  for (const word of words) {
    if (word.[1](prefix)) {
      count += 1;
    }
  }
  return count;
}

Drag options to blanks, or click blank then click option'

AstartsWith

Bincludes

CendsWith

Dsubstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'includes' or 'endsWith' instead of 'startsWith'.

The correct method to check if a word starts with a prefix is startsWith.

4fill in blank

hard

Fill both blanks to create a function that returns a list of words starting with the prefix.

DSA Typescript

function filterWords(words: string[], prefix: string): string[] {
  return words.[1](word => word.[2](prefix));
}

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Afilter

Bmap

CstartsWith

Dincludes

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'map' instead of 'filter' changes the array instead of selecting items.

Use filter to select words, and startsWith to check the prefix.

5fill in blank

hard

Fill all three blanks to create a function that returns a dictionary with counts of words starting with each prefix in prefixes array.

DSA Typescript

function countWordsByPrefixes(words: string[], prefixes: string[]): {[key: string]: number} {
  const result: {[key: string]: number} = {};
  for (const prefix of prefixes) {
    result[[1]] = words.filter(word => word.[2](prefix)).[3];
  }
  return result;
}

Drag options to blanks, or click blank then click option'

Aprefix

BstartsWith

Clength

Dincludes

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'includes' instead of 'startsWith' causes wrong counts.

We use the prefix as the key, filter words starting with it, and get the count using length.