Constructors and initialization in C Sharp (C#) - Time & Space Complexity

Time Complexity: Constructors and initialization

O(n)

Understanding Time Complexity

When we create objects using constructors, some steps run to set up the object.

We want to see how the time needed changes as we create more objects or initialize more data.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

public class Box
{
    public int[] Items;

    public Box(int size)
    {
        Items = new int[size];
        for (int i = 0; i < size; i++)
        {
            Items[i] = i * 2;
        }
    }
}

// Creating a Box object
Box myBox = new Box(1000);
    

This code creates a Box object and fills an array with values during construction.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The for-loop inside the constructor that fills the array.
• How many times: It runs once for each element in the array, so size times.

How Execution Grows With Input

As the size of the array grows, the number of steps to fill it grows too.

Input Size (n)	Approx. Operations
10	About 10 steps to fill the array
100	About 100 steps to fill the array
1000	About 1000 steps to fill the array

Pattern observation: The work grows directly with the size of the array; doubling the size doubles the work.

Final Time Complexity

Time Complexity: O(n)

This means the time to initialize grows in a straight line with the number of items we set up.

Common Mistake

[X] Wrong: "Constructors always run in constant time no matter what."

[OK] Correct: If a constructor does work like filling an array, the time depends on how much data it handles, so it grows with input size.

Interview Connect

Understanding how constructors scale helps you explain object setup costs clearly, a useful skill when discussing code efficiency.

Self-Check

"What if the constructor called another method that also loops over the array? How would the time complexity change?"