70. Climbing Stairs

70. Climbing Stairs

题目原文：

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?

思路：

设T(n)为爬n级阶梯的方案数。

T(1) = 1

T(2) = 2

T(n) = T(n-1) + T(n-2)

代码：

class Solution {
public:
int climbStairs(int n) {
if(n==1) return 1;
if(n==2) return 2;
int a[n+1];
for(int i=0;i<=n;i++) a[i]=0;
a[1]=1;
a[2]=2;
for(int i=3;i<=n;i++) a[i]=a[i-1]+a[i-2];
return a
;
}
};