Climbing Stairs - LeetCode

Climbing Stairs

1. Recursive:
We can use recursive way to solve this problem: O(n) = O(n - 1) + O(n - 2).

2. DP:
This method also very straightforward. dp[i] means how many ways to reach level i. So it would take O(n) time and O(n) space to solve the problem.

3. Two pointers:
We also can use to pointers to store the info. It is like DP. But the space is reduced to O(1).