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. 1 step + 1 step 2. 2 steps
Example 2:
Input: n = 3
Output: 3
Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step
Constraints:
1 <= n <= 45
Solution
# @param {Integer} n
# @return {Integer}
def climb_stairs(n)
return n if n < 2
cache = Array.new(n)
cache[0] = 1
cache[1] = 2
(2...n).each do |i|
cache[i] = cache[i - 1] + cache[i - 2]
end
cache[n - 1]
end