LeetCode-in-All
70. Climbing Stairs
Easy
You are climbing a staircase. It takes n steps to reach the top.
Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
Example 1:
Input: n = 2
Output: 2
Explanation: There are two ways to climb to the top.
-
1 step + 1 step
-
2 steps
Example 2:
Input: n = 3
Output: 3
Explanation: There are three ways to climb to the top.
-
1 step + 1 step + 1 step
-
1 step + 2 steps
-
2 steps + 1 step
Constraints:
1 <= n <= 45
Solution
defmodule Solution do
@spec climb_stairs(n :: integer) :: integer
def climb_stairs(1), do: 1
def climb_stairs(2), do: 2
def climb_stairs(n), do: do_climb_stairs(1, 2, n - 2)
defp do_climb_stairs(a, b, n) when n > 0, do: do_climb_stairs(b, a + b, n - 1)
defp do_climb_stairs(_, b, _), do: b
end