Find number of ways to go n steps with 1 or 2 steps

Problem:
Frog can jump 1 or 2 steps write the code to find out number of ways to go up to n steps.

Solution:

The number of ways to jump to n steps is the n-th Fibonacci number!

F[n] = F[n-1] + F[n-2]; 
F1 = 1; F2 = 2;

Example:

F[3] = F[2] + F[1]
1 1 1 part of F[2]
2 1 part of F[2]
1 2 part of F[1]

F[2]
1 1 
2

F[1]
1

Complexity:

time - O(n)
space - O(1) (for iterative approach)

Links and credits:
http://www.careercup.com/question?id=5950229446656000