Climbing Stairs 爬楼梯问题，每次可以走1或2步，爬上n层楼梯总方法 （变相fibonacci）

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?

当n=1时，有1种方法，即直接走1步

当n=2时，有2方法：连续走2步，或直接走两步

对于n，设f(n)为总方法，则 f(n) = f(n-1)+f(n-2)

ps:f(n-1)即第一次走一步的走法，

f(n-2)即第一次走两步的走法

归回fibnacci问题解法：

 class Solution {
 public:
     int climbStairs(int n) {
         if(n < )
             return -;
         int res[] = {,};
         if(n<)
             return res[n];

         int fib1 = ;
         int fib2 = ;

         int result = ;

         for(int i =  ; i <= n ; i++){
             result = fib1 + fib2;
             fib1 = fib2;
             fib2 = result;
         }

         return result;
     }
 };