│ You are given a positive integer N which represents the number of steps │ in a staircase. You can either climb 1 or 2 steps at a time. Write a │ function that returns the number of unique ways to climb the stairs. │def staircase(n): │ # Fill this in. │ │print staircase(4) │# 5 │print staircase(5) │# 8 │ │ Can you find a solution in O(n) time?