70 Climb 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.

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

class Solution {
    public int climbStairs(int n) {
        if (n <= 1) {
            return 1;
        }
        int f0 = 1;
        int f1 = 1;
        int res = 0;
        for (int i = 2; i <= n; i++) {
            res = f0 + f1;
            f0 = f1;
            f1 = res;
        }
        return res;
    }
}