Big-o-notation

Big O notation is a way to describe how fast an algorithm’s runtime or memory usage grows as the input size gets very large. It answers the question: ‘What happens when I give this algorithm 1,000 items instead of 10?’

It describes the shape of the curve on a graph, not the exact speed.

Documentation

See also List of Big-O for PHP functions, Simple Big-O Notations using PHP CLI, Algorithm Complexity & Big O Notation and Big O Cheat Sheet – Time Complexity Chart.

Related : Algorithm, Algorithmic Complexity, Data Structure