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?
Note: Given n will be a positive integer.
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
Solution in C++
class Solution { public: int climbStairs(int n) { if (n<=3) return n; int i1=2, i2=3; for(int i=4; i<n; i++) { int tmp=i1+i2; i1=i2; i2=tmp; } return i1+i2; } };