70. Climbing Stairs

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.

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