There are n stairs, a person standing at the bottom wants to reach the top. The person can climb either 1 or 2 stairs at a time. Count the number of ways, the person can reach the top.
There are several ways to solve this problem (recursive, iterative, dynamic programming, brute force). In this example, we use the dynamic programming fib implementation.
It's not always clear if 0 steps should be 1 path or 0 paths. You could argue either way: (a) there was no steps so there are no paths through the steps or (b) there was no steps so there is only 1 path through the 'steps'. In these examples, we opt for (a).
The simple implementation only supports 1 or 2 steps at a time, which means a simple call to fib works.
If more steps can be taken, it's advisable to use an iterative implementation. See staircaseIterative.ts for an example that supports 3 steps at a time, too.