Interview Q&A

Short answer: Use a foreach loop which iterates over the elements in sorted ascending order: foreach (var item in sortedSet)

Example code

{ Console.WriteLine(item); }

Real-world example (ShopNest)

When applying a coupon, ShopNest keeps used coupon codes in a HashSet<string> so “already used?” checks stay fast and unique.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: You can use a foreach loop over KeyValuePair<TKey, TValue> elements, which iterates in sorted key order: foreach (var kvp in sortedList) { Console.WriteLine($"Key: {kvp.Key}, Value: {kvp.Value}"); } You can also iterate over keys or values separately: foreach (var key in sortedList.Keys) { /* ... */ }

Example code

foreach (var value in sortedList.Values) { /* ... */ } 📘 C# SortedSet<T> – Interview Questions & Answers

Real-world example (ShopNest)

In ShopNest, an order page loads products with List<Product> so you can Add items to the cart and access them by index. Use IEnumerable<T> when you only need to loop (for example, printing invoice lines).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Adding or removing at the start or end: O(1) Adding or removing at an arbitrary position (if you already have the node reference): O(1) Searching for a node by value: O(n), because traversal is required

Real-world example (ShopNest)

In ShopNest, an order page loads products with List<Product> so you can Add items to the cart and access them by index. Use IEnumerable<T> when you only need to loop (for example, printing invoice lines).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: No, HashSet<T> does not allow duplicates. Attempting to add a duplicate value will return false and not change the set.

Example code

bool added = uniqueNumbers.Add(2); // returns false because 2 already exists

Real-world example (ShopNest)

When applying a coupon, ShopNest keeps used coupon codes in a HashSet<string> so “already used?” checks stay fast and unique.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the Peek() method. Example: int top = stack.Peek(); This is useful when you just want to inspect the top element without altering the stack.

Example code

Use the Peek() method. Example: int top = stack.Peek(); This is useful when you just want to inspect the top element without altering the stack.

Real-world example (ShopNest)

ShopNest uses a Queue<Order> for “orders waiting for payment confirmation,” and a Stack<Uri> for back-navigation in the admin UI.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the Peek() method to view the front element without removing it.

Example code

Queue<string> tasks = new Queue<string>(); tasks.Enqueue("Task1"); string nextTask = tasks.Peek(); // Returns "Task1", does not remove it Useful when you want to see what’s next without modifying the queue.

Real-world example (ShopNest)

ShopNest uses a Queue<Order> for “orders waiting for payment confirmation,” and a Stack<Uri> for back-navigation in the admin UI.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: The average time complexity is O(1) (constant time), thanks to hash-based indexing. However, in worst-case scenarios (rare), it can degrade to O(n).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Contains(item) IndexOf(item) Find(predicate) FindAll(predicate) Exists(predicate) BinarySearch(item) (for sorted lists) Example: bool hasItem = numbers.Contains(10);

Example code

int index = numbers.IndexOf(10);
var result = numbers.Find(x => x > 50);

Real-world example (ShopNest)

In ShopNest, an order page loads products with List<Product> so you can Add items to the cart and access them by index. Use IEnumerable<T> when you only need to loop (for example, printing invoice lines).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: IList<T> extends ICollection<T> and allows: Indexed access (like arrays) Inserting and removing at specific positions

Example code

IList<string> fruits = new List<string>(); fruits.Add("Apple"); fruits.Insert(0, "Banana"); // Insert at index 0 Console.WriteLine(fruits[1]); // Access by index Real-world use case: Use IList<T> when order matters and you need to access, insert, or remove elements at specific positions, like reordering tasks in a to-do list.

Real-world example (ShopNest)

In ShopNest, an order page loads products with List<Product> so you can Add items to the cart and access them by index. Use IEnumerable<T> when you only need to loop (for example, printing invoice lines).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Dictionary? Feature TryGetValue() Indexer (dictionary[key]) Safe? Yes – avoids exception No – throws if key doesn't exist Returns Boolean (and output value) Direct value Use case When unsure if key exists When key is guaranteed to exist if (dictionary.TryGetValue("Bob", out int age)) { Console.WriteLine(age); } //… dictionary["Unknown"]; // throws…… Dictionary? Feature TryGetValue() Indexer (dictionary[key]) Safe?…

Explain a bit more

Yes – avoids exception No – throws if key doesn't exist Returns Boolean (and output value) Direct value Use case When unsure if key exists When key is guaranteed to exist

Example code

if (dictionary.TryGetValue("Bob", out int age)) { Console.WriteLine(age); } // dictionary["Unknown"]; // throws KeyNotFoundException if missing Dictionary? Feature TryGetValue() Indexer (dictionary[key]) Safe? Yes – avoids exception No – throws if key doesn't exist Returns Boolean (and output value) Direct value Use case When unsure if key exists When key is guaranteed to exist Example: if (dictionary.TryGetValue("Bob", out int age)) { Console.WriteLine(age); } //… dictionary["Unknown"]; // throws… Dictionary? Feature TryGetValue() Indexer (dictionary[key]) Safe? Yes – avoids exception No – throws if key doesn't exist Returns Boolean (and output value) Direct value Use case When unsure if key exists When key is guaranteed to exist Example: if (dictionary.TryGetValue("Bob", out int age)) { Console.WriteLine(age); } // dictionary["Unknown"]; // throws KeyNotFoundException if missing

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Actually, SortedList<TKey, TValue> stores key-value pairs sorted by keys. To store items in a specific order, use the key to represent the sorting criteria. Keys must be unique and implement IComparable or provide a custom IComparer.

Example code

SortedList<int, string> sortedList = new SortedList<int, string>(); sortedList.Add(10, "Ten"); sortedList.Add(5, "Five"); sortedList.Add(20, "Twenty"); // Items automatically sorted by keys: 5, 10, 20 If you want to sort by custom criteria, implement an IComparer and pass it to the SortedList constructor.

Real-world example (ShopNest)

In ShopNest, an order page loads products with List<Product> so you can Add items to the cart and access them by index. Use IEnumerable<T> when you only need to loop (for example, printing invoice lines).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Due to the underlying balanced tree structure, these operations have O(log n) time complexity. 📘 C# Collection Initializers & LINQ – Interview Questions & Answers

Real-world example (ShopNest)

When applying a coupon, ShopNest keeps used coupon codes in a HashSet<string> so “already used?” checks stay fast and unique.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Operation LinkedList<T> List<T> Indexed access O(n) (no indexing) O(1) (direct access) Add/Remove at start/end O(1) O(n) (start), O(1) (end) Add/Remove in middle O(1) (with node ref) O(n) (shifts elements) Memory overhead Higher (extra pointers) Lower (array storage) Summary: Use LinkedList<T> when you need fast insertions/deletions anywhere and don’t require indexed access.

Explain a bit more

Use List<T> for fast random access and better memory efficiency. 📘 C# SortedList<TKey, TValue> – Interview Questions & Answers

Real-world example (ShopNest)

In ShopNest, an order page loads products with List<Product> so you can Add items to the cart and access them by index. Use IEnumerable<T> when you only need to loop (for example, printing invoice lines).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Union: Combines all unique elements from both sets set1.UnionWith(set2); Intersection: Keeps only elements present in both sets set1.IntersectWith(set2); Example: HashSet<int> set1 = new HashSet<int> { 1, 2, 3 };

Example code

HashSet<int> set2 = new HashSet<int> { 3, 4, 5 };
set1.UnionWith(set2); // set1 = {1, 2, 3, 4, 5}
set1.IntersectWith(set2); // set1 = {3, 4, 5}

Real-world example (ShopNest)

When applying a coupon, ShopNest keeps used coupon codes in a HashSet<string> so “already used?” checks stay fast and unique.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Peek() returns the top element without removing it. It’s helpful for: Conditional checks Previewing what's next Preventing accidental removal Example: if (stack.Count > 0)

Example code

{
var current = stack.Peek();
} Throws InvalidOperationException if the stack is empty.

Real-world example (ShopNest)

ShopNest uses a Queue<Order> for “orders waiting for payment confirmation,” and a Stack<Uri> for back-navigation in the admin UI.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the Clear() method to remove all elements. Example: tasks.Clear(); After calling Clear(), the queue is empty (Count == 0).

Example code

Use the Clear() method to remove all elements. Example: tasks.Clear(); After calling Clear(), the queue is empty (Count == 0).

Real-world example (ShopNest)

ShopNest uses a Queue<Order> for “orders waiting for payment confirmation,” and a Stack<Uri> for back-navigation in the admin UI.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Feature TryGetValue() Indexer (dictionary[key]) Safe? Yes – avoids exception No – throws if key doesn't exist Returns Boolean (and output value) Direct value Use case When unsure if key exists When key is guaranteed to exist

Example code

if (dictionary.TryGetValue("Bob", out int age)) { Console.WriteLine(age); } // dictionary["Unknown"]; // throws KeyNotFoundException if missing

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Method Purpose Add() Adds one item AddRange () Adds multiple items (collection) Example: list.Add(1); // One item list.AddRange(new[] { 2, 3, 4 }); // Multiple

Example code

Method Purpose Add() Adds one item AddRange () Adds multiple items (collection) Example: list.Add(1); // One item
list.AddRange(new[] { 2, 3, 4 }); // Multiple

Real-world example (ShopNest)

In ShopNest, an order page loads products with List<Product> so you can Add items to the cart and access them by index. Use IEnumerable<T> when you only need to loop (for example, printing invoice lines).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: These interfaces provide read-only access to collections: IReadOnlyCollection<T> provides Count and enumeration. IReadOnlyList<T> provides index-based access without modification.

Example code

IReadOnlyList<int> ids = new List<int> { 1, 2, 3 }; Console.WriteLine(ids[0]); // Access element // ids[0] = 10; // Compile-time error – read-only Real-world use case: Useful in APIs where you want to expose collection data but prevent consumers from modifying it—e.g., returning a list of supported currencies from a service.

Real-world example (ShopNest)

In ShopNest, an order page loads products with List<Product> so you can Add items to the cart and access them by index. Use IEnumerable<T> when you only need to loop (for example, printing invoice lines).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: dd()? Insert(index, item) adds an item at a specific index. Add(item) adds to the end of the list. list.Insert(0, 99); // Add at beginning list.Add(100); // Add at end dd()? Insert(index, item) adds an item at a specific index. Add(item) adds to the end of the list.

Example code

list.Insert(0, 99); // Add at beginning… list.Add(100); // Add at end dd()? Insert(index, item) adds an item at a specific index. Add(item) adds to the end of the list. Example: list.Insert(0, 99); // Add at beginning list.Add(100); // Add at end dd()? Insert(index, item) adds an item at a specific index. Add(item) adds to the end of the list. Example: list.Insert(0, 99); // Add at beginning… list.Add(100); // Add at end

Real-world example (ShopNest)

In ShopNest, an order page loads products with List<Product> so you can Add items to the cart and access them by index. Use IEnumerable<T> when you only need to loop (for example, printing invoice lines).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Method Purpose Return Value Add(item) Adds item if not already present true if added, false if duplicate Contains(it em) Checks if item exists in the set true if found, false otherwise

Real-world example (ShopNest)

When applying a coupon, ShopNest keeps used coupon codes in a HashSet<string> so “already used?” checks stay fast and unique.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the Count property. if (stack.Count == 0)

Example code

{ Console.WriteLine("Stack is empty"); } Unlike some languages, C# stacks do not provide an IsEmpty property.

Real-world example (ShopNest)

ShopNest uses a Queue<Order> for “orders waiting for payment confirmation,” and a Stack<Uri> for back-navigation in the admin UI.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use a foreach loop. Iteration does not modify the queue. Example: foreach (var order in orders)

Example code

{ Console.WriteLine(order); } You can also use .ToArray() if needed: string[] items = orders.ToArray();

Real-world example (ShopNest)

ShopNest uses a Queue<Order> for “orders waiting for payment confirmation,” and a Stack<Uri> for back-navigation in the admin UI.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: dictionary.Keys – returns a collection of all keys dictionary.Values – returns a collection of all values Example: foreach (var key in dictionary.Keys) Console.WriteLine(key); foreach (var value in dictionary.Values) Console.WriteLine(value);

Example code

dictionary.Keys – returns a collection of all keys dictionary.Values – returns a collection of all values Example: foreach (var key in dictionary.Keys) Console.WriteLine(key); foreach (var value in dictionary.Values) Console.WriteLine(value);

Real-world example (ShopNest)

ShopNest caches product prices in a Dictionary<string, decimal> keyed by SKU so checkout can look up a price in O(1) instead of scanning a list.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Insert(index, item) adds an item at a specific index. Add(item) adds to the end of the list. Example: list.Insert(0, 99); // Add at beginning list.Add(100); // Add at end

Example code

Insert(index, item) adds an item at a specific index. Add(item) adds to the end of the list. Example: list.Insert(0, 99); // Add at beginning
list.Add(100); // Add at end

Real-world example (ShopNest)

In ShopNest, an order page loads products with List<Product> so you can Add items to the cart and access them by index. Use IEnumerable<T> when you only need to loop (for example, printing invoice lines).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.