Day 39.1.txt

70. Climbing Stairs

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
 

Constraints:

1 <= n <= 45



class Solution {
    public int climbStairs(int n) {
        if(n==1)
            return 1;
        else if(n==2)
            return 2;
        else
        {
            int a=1,b=2,c=0,i;
            for(i=3;i<=n;i++)
            {
                c=a+b;
                a=b;
                b=c;
            }
            return c;
        }
    }
}