Count Words with Given Prefix in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Javascript

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

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

Aincludes

BstartsWith

CendsWith

DindexOf

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using 'endsWith' which checks the end of the word.

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 Javascript

function countWords(words, prefix) {
  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'

AstartsWith

BindexOf

CendsWith

Dincludes

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'includes' which counts words containing prefix anywhere.

Using 'endsWith' which checks the end of the word.

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

3fill in blank

hard

Fix the error in the code to correctly count words with the prefix.

DSA Javascript

function countWords(words, prefix) {
  return words.filter(word => word.[1](prefix)).length;
}

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

AendsWith

Bincludes

CstartsWith

DindexOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'includes' which matches anywhere in the word.

Using 'endsWith' which checks the end of the word.

The filter method keeps words starting with the prefix using startsWith, then counts them.

4fill in blank

hard

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

DSA Javascript

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

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

Afilter

Bmap

CstartsWith

Dincludes

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using 'includes' which matches prefix anywhere, not just start.

filter selects words where startsWith returns true for the prefix.

5fill in blank

hard

Fill all three blanks to create a function that returns the count of words starting with the prefix using reduce.

DSA Javascript

function countWordsReduce(words, prefix) {
  return words.reduce((count, word) => {
    return count + (word.[1](prefix) ? [2] : [3]);
  }, 0);
}

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

AstartsWith

B1

C0

Dincludes

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'includes' instead of 'startsWith'.

Adding wrong values instead of 1 or 0.

The reduce method adds 1 to count if the word starts with prefix, else adds 0.