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?
class Solution { public: int climbStairs(int n) { if(n<=2) return n; int pre1 = 2; int pre2 = 1; int res = 0; for(int i=3;i<=n;++i){ res = pre1+pre2; pre2 = pre1; pre1 = res; } return res; } };
原文：http://www.cnblogs.com/zengzy/p/5060472.html