chal_70.py

class Solution(object):
    def climb_stairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        if n == 1:
            return 1

        results = [0] * n
        for step in range(n - 1, -1, -1):
            if step == n - 1 or step == n - 2:
                results[step] = 1
            else:
                results[step] = results[step + 1] + results[step + 2]
        return results[0] + results[1]


# Test cases
sol = Solution()

n = 2
assert sol.climb_stairs(n) == 2

n = 3
assert sol.climb_stairs(n) == 3

n = 4
assert sol.climb_stairs(n) == 5

n = 5
assert sol.climb_stairs(n) == 8

n = 6
assert sol.climb_stairs(n) == 13