Before we delve into the multiple runtime cases, let’s see the different common runtimes a program could have. Below is a list of common runtimes that run from fastest to slowest.
- Θ(1). This is constant runtime. This is the runtime when a program will always do the same thing regardless of the input. For instance, a program that only prints “hello, world” runs in
Θ(1)because the program will always just print “hello, world”.
- Θ(log N). This is logarithmic runtime. You will see this runtime in search algorithms.
- Θ(N). This is linear runtime. You will often see this when you have to iterate through an entire dataset.
- Θ(N*logN). You will see this runtime in sorting algorithms.
- Θ(N2). This is an example of a polynomial runtime. When N is raised to the 2nd power, it’s known as a quadratic runtime. You will see this runtime when you have to search through a two-dimensional dataset (like a matrix) or nested loops.
- Θ(2N). This is exponential runtime. You will often see this runtime in recursive algorithms (Don’t worry if you don’t know what that is yet!).
- Θ(N!). This is factorial runtime. You will often see this runtime when you have to generate all of the different permutations of something. For instance, a program that generates all the different ways to order the letters “abcd” would run in this runtime.