The efficiency of constant runtime algorithms remains fixed as we increase the input size. Many examples of these exist. Consider, for example, accessing an element in an array. Access performance doesn't depend on the size of the array, so as we increase the size of the array, the access speed stays constant.

Consider the code in Snippet 1.9. The number of operations performed remains constant, irrespective of the size of the input radius. Such an algorithm is said to have a runtime complexity of O(1). The code snippet is as follows:

private double circleCircumference(int radius) {
  return 2.0 * Math.PI * radius;
}  

Constant complexity algorithms are the most desirable out of all the complexity classes for the best scaling. Many of the simple mathematical functions, such as finding the distance between two points and mapping a three-dimensional coordinate to a two-dimensional one, all fall under this class.