You are climbing a stair case. It takes n steps to reach to 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: 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps
Example 2:
Input: 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:
class Solution {
public int climbStairs(int n) {
int prevPrev = 1;
int prev = 1;
for (int i = 2; i <= n; i ++) {
int curr = prevPrev + prev;
prevPrev = prev;
prev = curr;
}
return prev;
}
}