LeetCode：Climbing Stairs解法

题目：

         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?

代码：

int climbStairs(int n)
{
	if (n == 1)
		return 1;

	if (n == 2)
		return 2;

	int res = 0;
	int f_1 = 1;
	int f_2 = 2;
	for (int i = 3; i <= n; ++i)
	{
		res = f_1 + f_2;
		f_1 = f_2;
		f_2 = res;
	}
	return res;
}