Tutorials Data Structures and Algorithms in C#
List<T> Dynamic Arrays
List<T> Dynamic Arrays: free step-by-step lesson with examples, common mistakes, and interview tips — part of Data Structures and Algorithms in C# on Toolliyo Academy.
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Data Structures and Algorithms in C# · Lesson 12 of 120
List Dynamic Arrays
Foundations & Arrays → Lists, Hash, Trees → Graphs & DP → Advanced & Projects
Foundations & Arrays · 1 — Basics · ~6 min · Arrays and Strings
What is this?
List
Why should you care?
Most C# interview array problems use List or int[] — know the cost of Insert(0, x).
See it live — copy this example
Run snippets in a .NET console app, LINQPad, or https://dotnetfiddle.net. Write Big O above every solution.
var xs = new List<int>(capacity: 8);
xs.Add(10);
xs.Add(20);
xs.Insert(0, 5); // shifts right — O(n)
Console.WriteLine(string.Join(',', xs));What happened?
- Capacity reduces reallocations.
- Insert at front is expensive.
- Prefer Add at end when possible.
Practice next
- Run with and without capacity.
- Insert 1000 times at index 0 and feel the slowdown.
- Prefer Add + Reverse when building reversed sequences.
- Try RemoveAt(0).
- Use RemoveAll with a predicate.
Remember
List ≈ dynamic array. End adds are cheap. Middle edits are costly.
Building a buffer
Collect results then reverse.
Outcome: Add + Reverse beats Insert(0).
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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