EasyDp
Climbing Stairs
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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
Examples
Example 1
Input: n = 2
Output: 2
Explanation: Two ways: (1+1) or (2).
Example 2
Input: n = 5
Output: 8
Explanation: Eight ways: 1+1+1+1+1, 1+1+1+2, 1+1+2+1, 1+2+1+1, 2+1+1+1, 1+2+2, 2+1+2, 2+2+1.
Constraints
- -1 <= n <= 45
Optimal Complexity
Time
O(n)
Space
O(1)
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