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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to sort the array in ascending order using Array.Sort.

DSA C#

int[] numbers = {5, 3, 8, 1, 2};
Array.[1](numbers);
foreach (int num in numbers) {
    Console.Write(num + " ");
}

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

ACopy

BSort

CClear

DReverse

Attempts:

3 left

💡 Hint

Common Mistakes

Using Array.Reverse instead of Array.Sort.

Trying to sort without calling any method.

Array.Sort sorts the array in ascending order. Reverse would reverse the array, Clear would reset elements, and Copy copies elements.

2fill in blank

medium

Complete the code to find if the number 4 exists in the sorted array using Array.BinarySearch.

DSA C#

int[] sortedNumbers = {1, 2, 3, 5, 8};
int index = Array.[1](sortedNumbers, 4);
Console.WriteLine(index >= 0 ? "Found" : "Not Found");

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

AIndexOf

BFind

CBinarySearch

DSearch

Attempts:

3 left

💡 Hint

Common Mistakes

Using IndexOf, which performs linear search.

Using Find which is not a static Array method.

Array.BinarySearch searches a sorted array efficiently (logarithmic time). Find is not a static method on Array, IndexOf performs linear search, and Search does not exist.

3fill in blank

hard

Fix the error in the code to correctly sort the list of strings alphabetically.

DSA C#

List<string> fruits = new List<string> {"banana", "apple", "cherry"};
fruits.[1]();
foreach (string fruit in fruits) {
    Console.Write(fruit + " ");
}

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

AArrange

BSortBy

COrderBy

DSort

Attempts:

3 left

💡 Hint

Common Mistakes

Using OrderBy without assigning the result back.

Using non-existent methods like Arrange or SortBy.

List has a Sort() method to sort elements in place. OrderBy is a LINQ method that returns a new sequence, Arrange and SortBy do not exist.

4fill in blank

hard

Fill both blanks to create a dictionary that maps each word to its length.

DSA C#

string[] words = {"cat", "elephant", "dog", "lion"};
var wordLengths = words.ToDictionary(word => [1], word => word.[2]);

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

Aword

BLength

CCount

Dword.Length

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'word.Length' for BLANK_1, which would make keys the lengths instead of words.

Using Count which is not a property of string.

The key selector is the word itself, so 'word'. The value selector is the length property, 'Length'. 'word.Length' does not fit the blank format, as the blank expects a simple identifier.

5fill in blank

hard

Fill all three blanks to create a dictionary of words and their lengths, but only include words longer than 3 characters.

DSA C#

string[] words = {"cat", "elephant", "dog", "lion"};
var filtered = words.Where(word => word.[1] > [2]);
var wordLengths = filtered.ToDictionary([3] => [3], [3] => [3].Length);

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

ALength

B3

Cword

DCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using Count instead of Length for strings.

Using a number other than 3 for filtering.

The Where clause filters words with Length > 3. The ToDictionary uses 'word' as the key selector and value selector uses word.Length.

Practice

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

easy

A. It removes duplicate data automatically

B. It organizes data to make searching and comparisons faster

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 a specific order, such as ascending or descending, which helps algorithms work efficiently.

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

   When data is sorted, algorithms like binary search can quickly find elements, and comparisons become simpler.

3. Final Answer:

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

4. Quick Check:

   Sorting improves search speed = A [OK]

Hint: Sorting arranges data to speed up other algorithms [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 integer array named numbers in C#?

easy

A. Array.Sort(numbers);

B. numbers.sort();

C. sort(numbers);

D. Array.sorted(numbers);

Solution

1. Step 1: Recall C# array sorting method

   In C#, the static method Array.Sort() is used to sort arrays in place.

2. Step 2: Check syntax correctness

   Array.Sort(numbers); correctly calls the method on the array numbers. Other options are invalid method calls or do not exist.

3. Final Answer:

   Array.Sort(numbers); -> Option A

4. Quick Check:

   C# array sorting uses Array.Sort() = D [OK]

Hint: Use Array.Sort(array) to sort arrays in C# [OK]

Common Mistakes:

• Using lowercase sort() method on arrays
• Calling non-existent methods like sorted()
• Confusing list sorting syntax with array sorting

3. What will be the output of the following C# code?

int[] arr = {5, 3, 8, 1};
Array.Sort(arr);
foreach (int num in arr) {
    Console.Write(num + " ");
}

medium

A. 1 3 5 8

B. 5 3 8 1

C. 8 5 3 1

D. 3 1 5 8

Solution

1. Step 1: Understand Array.Sort effect

   The Array.Sort(arr); call sorts the array in ascending order: {1, 3, 5, 8}.

2. Step 2: Trace the foreach loop output

   The loop prints each element followed by a space, resulting in "1 3 5 8 ".

3. Final Answer:

   1 3 5 8 -> Option A

4. Quick Check:

   Sorted array printed in ascending order = B [OK]

Hint: Array.Sort sorts ascending; print shows sorted elements [OK]

Common Mistakes:

• Assuming original order is printed
• Confusing ascending with descending order
• Missing spaces in output

4. The following code is intended to sort an array but throws a runtime error. What is the problem?

int[] data = null;
Array.Sort(data);
Console.WriteLine("Sorted");

medium

A. The array must be initialized with values before sorting

B. Array.Sort requires a list, not an array

C. Array.Sort cannot sort null arrays and throws an exception

D. Console.WriteLine is missing parentheses

Solution

1. Step 1: Identify the null array usage

   The variable data is assigned null, meaning it points to no array.

2. Step 2: Understand Array.Sort behavior on null

   Calling Array.Sort(null) causes a ArgumentNullException because the method expects a valid array reference.

3. Final Answer:

   Array.Sort cannot sort null arrays and throws an exception -> Option C

4. Quick Check:

   Sorting null array causes exception = A [OK]

Hint: Array.Sort needs a valid array, not null [OK]

Common Mistakes:

• Thinking Array.Sort accepts null arrays
• Confusing array and list types
• Misreading Console.WriteLine syntax

5. You have two sorted arrays:
int[] a = {1, 4, 7};
int[] b = {2, 5, 6};
Which approach best uses sorting to efficiently merge them into one sorted array?

hard

A. Concatenate both arrays then sort the combined array

B. Sort each array separately again before merging

C. Reverse both arrays then merge

D. Use a two-pointer technique to merge without extra sorting

Solution

1. Step 1: Recognize arrays are already sorted

   Both arrays a and b are sorted, so no need to sort again.

2. Step 2: Apply two-pointer merge technique

   Using two pointers, one for each array, we compare elements and build a merged sorted array efficiently without extra sorting.

3. Final Answer:

   Use a two-pointer technique to merge without extra sorting -> Option D

4. Quick Check:

   Merge sorted arrays with two pointers = C [OK]

Hint: Merge sorted arrays with two pointers, no extra sort needed [OK]

Common Mistakes:

• Sorting combined array wastes time
• Sorting arrays again is unnecessary
• Reversing arrays breaks sorted order