LeetCode 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?

递归导致超时，所以非递归。

public  long climbStairs(long n) {
		if (n <= 2) return n;
		long f1 = 1;
		long f2 = 2;
		long f3 = 0;
		int i = 3;
		while (i++ <= n) {
			f3 = f1 + f2;
			f1 = f2;
			f2 = f3;
		}
		return f3;
	}