Why Sorting Matters and How It Unlocks Other Algorithms in DSA Javascript - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to sort the array in ascending order using the built-in method.

DSA Javascript

const numbers = [5, 3, 8, 1];
numbers.sort([1]);
console.log(numbers);

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

A() => a - b

B(a, b) => b - a

C(a, b) => a - b

D() => b - a

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function without parameters causes incorrect sorting.

Using (a, b) => b - a sorts in descending order, not ascending.

The sort method requires a comparison function with two parameters a and b. Returning a - b sorts ascending.

2fill in blank

medium

Complete the code to find the median after sorting the array.

DSA Javascript

const arr = [7, 2, 5, 3];
arr.sort([1]);
const mid = Math.floor(arr.length / 2);
const median = arr.length % 2 !== 0 ? arr[mid] : (arr[mid - 1] + arr[mid]) / 2;
console.log(median);

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

A(a, b) => a - b

B() => a - b

C(a, b) => b - a

D() => b - a

Attempts:

3 left

💡 Hint

Common Mistakes

Sorting descending changes the median calculation.

Not providing a comparison function sorts elements as strings.

Sorting ascending with (a, b) => a - b is needed to find the correct median.

3fill in blank

hard

Fix the error in the code to correctly sort an array of strings by length.

DSA Javascript

const words = ['apple', 'dog', 'banana', 'cat'];
words.sort((a, b) => [1]);
console.log(words);

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

Ab - a

Bb.length - a.length

Ca - b

Da.length - b.length

Attempts:

3 left

💡 Hint

Common Mistakes

Using a - b or b - a compares strings incorrectly.

Sorting descending when ascending is needed.

To sort strings by length ascending, subtract b.length from a.length.

4fill in blank

hard

Fill both blanks to create a sorted array of unique numbers.

DSA Javascript

const nums = [4, 2, 5, 2, 3, 4];
const uniqueSorted = [...new Set(nums)].sort([1]);
console.log(uniqueSorted);

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

A(a, b) => b - a

B(a, b) => a - b

C() => a - b

D() => b - a

Attempts:

3 left

💡 Hint

Common Mistakes

Not using a comparison function sorts numbers as strings.

Using arrow functions without parameters causes errors.

Use (a, b) => a - b to sort numbers ascending after removing duplicates.

5fill in blank

hard

Fill all three blanks to create a sorted array of objects by age, then map to names.

DSA Javascript

const people = [
  { name: 'Alice', age: 30 },
  { name: 'Bob', age: 25 },
  { name: 'Carol', age: 35 }
];
const sortedNames = people.sort((a, b) => [1]).map(person => person.[2]).filter(name => name.length > [3]);
console.log(sortedNames);

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

Aa.age - b.age

Bname

C3

Db.age - a.age

Attempts:

3 left

💡 Hint

Common Mistakes

Sorting descending when ascending is needed.

Mapping to wrong property name.

Filtering with incorrect length value.

Sort ascending by age with a.age - b.age, map to 'name', and filter names longer than 3 characters.

Practice

1. Why is sorting an important step before applying many algorithms in data processing?

easy

A. It organizes data to make searching and comparisons faster

B. It removes duplicate data automatically

C. It encrypts data for security

D. It compresses data to save space

Solution

1. Step 1: Understand sorting's role in data organization

   Sorting arranges data in order, which helps algorithms work efficiently by reducing unnecessary checks.

2. Step 2: Connect sorting to faster searching and comparisons

   When data is sorted, algorithms like binary search can quickly find elements, improving speed.

3. Final Answer:

   It organizes data to make searching and comparisons faster -> Option A

4. Quick Check:

   Sorting helps algorithms run faster = A [OK]

Hint: Sorting arranges data for faster search and comparison [OK]

Common Mistakes:

• Thinking sorting removes duplicates automatically
• Confusing sorting with encryption or compression

2. Which of the following is the correct syntax to sort an array arr in JavaScript in ascending order?

easy

A. arr.sort((a, b) => a - b)

B. arr.sort()

C. arr.sort((a, b) => b - a)

D. arr.sorted()

Solution

1. Step 1: Recall JavaScript's default sort behavior

   By default, arr.sort() sorts elements as strings, which can misorder numbers.

2. Step 2: Use a compare function for numeric ascending order

   The compare function (a, b) => a - b sorts numbers correctly in ascending order.

3. Final Answer:

   arr.sort((a, b) => a - b) -> Option A

4. Quick Check:

   Numeric ascending sort uses compare function = B [OK]

Hint: Use compare function (a, b) => a - b for numeric ascending sort [OK]

Common Mistakes:

• Using arr.sort() alone for numeric arrays
• Using arr.sorted() which is not a valid method
• Using (a, b) => b - a which sorts descending

3. What will be the output of the following JavaScript code?

const arr = [5, 3, 8, 1];
arr.sort();
console.log(arr);

medium

A. [1, 3, 5, 8]

B. [1, 3, 5, 8] but sorted as strings

C. [1, 10, 3, 5, 8]

D. [1, 3, 5, 8, 10]

Solution

1. Step 1: Understand default sort behavior in JavaScript

   Without a compare function, arr.sort() sorts elements as strings, not numbers.

2. Step 2: Apply string comparison to the array

   Sorting [5,3,8,1] as strings results in [1, 3, 5, 8] which matches numeric order here but is due to string comparison.

3. Final Answer:

   [1, 3, 5, 8] but sorted as strings -> Option B

4. Quick Check:

   Default sort is string-based = D [OK]

Hint: Default sort treats numbers as strings unless compare function used [OK]

Common Mistakes:

• Assuming default sort sorts numbers numerically
• Expecting extra elements in output
• Confusing string sort with numeric sort

4. The following code is intended to sort an array of numbers in ascending order. What is the error?

const numbers = [10, 2, 30, 4];
numbers.sort((a, b) => b - a);
console.log(numbers);

medium

A. The array is not declared correctly

B. The sort method is misspelled

C. The compare function sorts in descending order, not ascending

D. The console.log statement is missing parentheses

Solution

1. Step 1: Analyze the compare function used

   The compare function (a, b) => b - a sorts numbers in descending order.

2. Step 2: Check the intended sorting order

   The question wants ascending order, so the compare function should be (a, b) => a - b.

3. Final Answer:

   The compare function sorts in descending order, not ascending -> Option C

4. Quick Check:

   Compare function direction controls sort order = A [OK]

Hint: Check compare function signs for ascending vs descending [OK]

Common Mistakes:

• Confusing ascending and descending compare functions
• Thinking sort method is misspelled
• Ignoring parentheses in console.log

5. You have two sorted arrays: A = [1, 3, 5] and B = [2, 4, 6]. Which approach best uses sorting to efficiently merge them into one sorted array?

hard

A. Concatenate A and B, then sort the combined array

B. Sort A and B separately again before merging

C. Reverse both arrays and then merge

D. Use two pointers to merge A and B in one pass without extra sorting

Solution

1. Step 1: Understand the problem of merging two sorted arrays

   Since both arrays are already sorted, merging can be done efficiently by comparing elements one by one.

2. Step 2: Use two pointers to merge without extra sorting

   Two pointers start at the beginning of each array and pick the smaller element to build the merged array in sorted order.

3. Final Answer:

   Use two pointers to merge A and B in one pass without extra sorting -> Option D

4. Quick Check:

   Merging sorted arrays uses two-pointer technique = C [OK]

Hint: Merge sorted arrays with two pointers for efficiency [OK]

Common Mistakes:

• Sorting concatenated arrays unnecessarily
• Sorting arrays again before merging
• Reversing arrays which breaks order