问题：
?
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?
分析：
该问题是符合斐波那契数列的，具体分析见《剑指offer》。
int climbStairs(int n) {
if(n <= 2) return n;
int f1 = 1;
int f2 = 2;
int f3;
for(int i = 3; i <= n; ++i)
{
f3 = f2 + f1;
f1 = f2;
f2 = f3;
}
return f3;
}