Python/dynamic_programming/climbing_stairs.py

#!/usr/bin/env python3


def climb_stairs(n: int) -> int:
    """
    LeetCdoe No.70: Climbing Stairs
    Distinct ways to climb a n step staircase where
    each time you can either climb 1 or 2 steps.

    Args:
        n: number of steps of staircase

    Returns:
        Distinct ways to climb a n step staircase

    Raises:
        AssertionError: n not positive integer

    >>> climb_stairs(3)
    3
    >>> climb_stairs(1)
    1
    >>> climb_stairs(-7)  # doctest: +ELLIPSIS
    Traceback (most recent call last):
        ...
    AssertionError: n needs to be positive integer, your input -7
    """
    fmt = "n needs to be positive integer, your input {}"
    assert isinstance(n, int) and n > 0, fmt.format(n)
    if n == 1:
        return 1
    dp = [0] * (n + 1)
    dp[0], dp[1] = (1, 1)
    for i in range(2, n + 1):
        dp[i] = dp[i - 1] + dp[i - 2]
    return dp[n]


if __name__ == "__main__":
    import doctest

    doctest.testmod()