LeetCode Climbing Stairs

就是斐波那契。

int climbStairs(int n) {
	if(n<=2)
		return n;
	int first=1,second=2;
	int ret;
	while(n>=3)
	{
		ret = first + second;
		first = second;
		second = ret;
		n--;
	}
	return ret;
}