【LeetCode OJ】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?

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