Coding Challenges and Assessment Interview Questions for .NET Developers

In this section, we present a variety of coding challenges and assessment interview questions typically encountered in .NET development roles. These questions cover a range of difficulties, from basic to advanced, and include both problem statements and solutions. These exercises will help you prepare for technical interviews and coding assessments.

1. Reverse a Linked List

Problem Statement:

Given the head of a singly linked list, reverse the list, and return the reversed list.

Solution:

public class ListNode

{

    public int val;

    public ListNode next;

    public ListNode(int val=0, ListNode next=null)

    {

        this.val = val;

        this.next = next;

    }

}

public ListNode ReverseList(ListNode head)

{

    ListNode prev = null;

    ListNode current = head;

    while (current != null)

    {

        ListNode nextTemp = current.next;

        current.next = prev;

        prev = current;

        current = nextTemp;

    }

    return prev;

}        

2. Two Sum Problem

Problem Statement:

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution, and you may not use the same element twice.

Solution:

public int[] TwoSum(int[] nums, int target)

{

    Dictionary<int, int> dict = new Dictionary<int, int>();

    for (int i = 0; i < nums.Length; i++)

    {

        int complement = target - nums[i];

        if (dict.ContainsKey(complement))

        {

            return new int[] { dict[complement], i };

        }

        dict[nums[i]] = i;

    }

    return new int[0];

}        

3. Find the Longest Substring Without Repeating Characters

Problem Statement:

Given a string s, find the length of the longest substring without repeating characters.

Solution:

public int LengthOfLongestSubstring(string s)

{

    int n = s.Length;

    int maxLength = 0;

    Dictionary<char, int> indexMap = new Dictionary<char, int>();

    int start = 0;

    for (int end = 0; end < n; end++)

    {

        if (indexMap.ContainsKey(s[end]))

        {

            start = Math.Max(indexMap[s[end]] + 1, start);

        }

        indexMap[s[end]] = end;

        maxLength = Math.Max(maxLength, end - start + 1);

    }

    return maxLength;

}        

4. Merge Two Sorted Lists

Problem Statement:

Merge two sorted linked lists and return it as a sorted list. The list should be made by splicing together the nodes of the first two lists.

Solution:

public ListNode MergeTwoLists(ListNode l1, ListNode l2)

{

    ListNode dummy = new ListNode(0);

    ListNode current = dummy;

    while (l1 != null && l2 != null)

    {

        if (l1.val <= l2.val)

        {

            current.next = l1;

            l1 = l1.next;

        }

        else

        {

            current.next = l2;

            l2 = l2.next;

        }

        current = current.next;

    }

    if (l1 != null)

    {

        current.next = l1;

    }

    else

    {

        current.next = l2;

    }

    return dummy.next;

}        

5. Find the Median of Two Sorted Arrays

Problem Statement:

Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays.

Solution:

public double FindMedianSortedArrays(int[] nums1, int[] nums2)

{

    int m = nums1.Length;

    int n = nums2.Length;

    if (m > n) return FindMedianSortedArrays(nums2, nums1); // Ensure nums1 is the smaller array

    int low = 0, high = m, halfLen = (m + n + 1) / 2;

    while (low <= high)

    {

        int i = (low + high) / 2;

        int j = halfLen - i;

        if (i < m && nums2[j - 1] > nums1[i])

        {

            low = i + 1; // i is too small

        }

        else if (i > 0 && nums1[i - 1] > nums2[j])

        {

            high = i - 1; // i is too large

        }

        else

        {

            int maxLeft = 0;

            if (i == 0) { maxLeft = nums2[j - 1]; }

            else if (j == 0) { maxLeft = nums1[i - 1]; }

            else { maxLeft = Math.Max(nums1[i - 1], nums2[j - 1]); }

            if ((m + n) % 2 == 1) return maxLeft;

            int minRight = 0;

            if (i == m) { minRight = nums2[j]; }

            else if (j == n) { minRight = nums1[i]; }

            else { minRight = Math.Min(nums1[i], nums2[j]); }

            return (maxLeft + minRight) / 2.0;

        }

    }

    throw new ArgumentException("Input arrays are not valid.");

}        

Interview Tips for Coding Challenges

1. Understand the Problem Statement: Ensure you fully understand the question and clarify any ambiguities before starting to code.

2. Start with a Plan: Outline your approach before diving into coding. Write pseudo-code or explain your logic to the interviewer.

3. Edge Cases: Consider edge cases and test your solution against them.

4. Time Complexity: Be mindful of the time complexity of your solution. Aim for the most efficient approach possible.

5. Code Clarity: Write clean and readable code. Use meaningful variable names and include comments if necessary.

6. Test Your Code: If the environment allows, test your code with different inputs to ensure its correctness.

Common Interview Questions and Answers

1. What is the difference between == and Equals() in C?

Answer:

The == operator compares object references, while the Equals() method compares the contents of the objects. For value types, == and Equals() usually give the same result, but for reference types, == checks if both variables point to the same object, whereas Equals() can be overridden to provide custom equality logic.

2. What is polymorphism in C?

Answer:

Polymorphism is a concept in object-oriented programming that allows methods to do different things based on the object it is acting upon. In C, polymorphism can be achieved through method overloading and method overriding.

3. Explain the difference between an abstract class and an interface.

Answer:

An abstract class can have implementations for some of its members (methods), but an interface cannot have any implementation. Abstract classes are used when you want to provide a common base class for derived classes, while interfaces are used to define a contract that other classes must implement.

4. What is dependency injection?

Answer:

Dependency injection is a design pattern used to implement IoC (Inversion of Control). It allows an object to receive its dependencies from an external source, rather than creating them itself. This promotes loose coupling and makes it easier to manage and test your application.

5. How does garbage collection work in .NET?

Answer:

The .NET garbage collector manages the allocation and release of memory for applications. It automatically releases memory occupied by objects that are no longer in use, reclaiming resources and preventing memory leaks. The garbage collector uses generations to manage memory more efficiently.

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