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?

这是一个简单的Fibonaci问题，只是前三个元素应为0，1，2.

public int climbStairs(int n) {
if(n<=2)return n;
long one=1,two=2,now=0;
for(int i=3;i<=n;i++){
now=one+two;
one=two;
two=now;
}
return (int) now;
}