Create Climbing Stairs

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?

开始使用常规的递归解法，但是时间复杂度通不过，于是用数组存储相加的方法，时间复杂度为O(n)。时间复杂度更优。