How PHP executes on the server - Performance & Efficiency

Time Complexity: How PHP executes on the server

O(n)

Understanding Time Complexity

When PHP runs on a server, it processes code step-by-step to create a web page.

We want to see how the time it takes grows as the code or input gets bigger.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

<?php
$numbers = [1, 2, 3, 4, 5];
$sum = 0;
foreach ($numbers as $num) {
    $sum += $num;
}
echo $sum;
?>

This code adds up all numbers in an array and prints the total.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping through each number in the array.
• How many times: Once for each number in the array.

How Execution Grows With Input

As the array gets bigger, the loop runs more times, adding each number.

Input Size (n)	Approx. Operations
10	10 additions
100	100 additions
1000	1000 additions

Pattern observation: The work grows directly with the number of items.

Final Time Complexity

Time Complexity: O(n)

This means the time to finish grows in a straight line with the input size.

Common Mistake

[X] Wrong: "The loop runs a fixed number of times no matter the input size."

[OK] Correct: The loop runs once for each item, so if the array grows, the loop runs more times.

Interview Connect

Understanding how PHP runs code step-by-step helps you explain how your programs handle bigger data smoothly.

Self-Check

"What if we replaced the loop with a function that calls itself for each item? How would the time complexity change?"