LeetCode之7 Climbing Stairs
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?

解析：本题目主要考虑递归和DP两种思想；但是递归的时间太长，大数时太耗时间，故采用DP的思想；利用一个含有3个整形变量的数组进行不断的操作，节省空间和时间的消耗；

代码如下：

 int climbStairs(int n) {            int  s[]={0,1,2};      if(n<=2) return s[n];            int num=2;      while(num++<n){              s[num%3]=s[(num+1)%3]+s[(num+2)%3];      }            return s[n%3];                            }