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;
}
};