[leetcode] climb stairs [70]

problem :  Suppose you're climbing the stairs , need n To reach the roof . Every time you climb 1 or 2 A stair , How many different ways can you climb to the top of the building ？

Example 1

Input : n = 2
Output : 2
explain : There are two ways to climb to the top
         ① 1 rank +1 rank
         ② 2 rank

Example 2

Input : n = 3
Output : 3
explain : There are three ways to climb to the top .
         ①1 rank +1 rank +1 rank
         ②1 rank +2 rank
         ③2 rank +1 rank

#  solution 1
def climbStairs(n):
    if n <= 2:
        return n
    else:
        return climbStairs(n-1) + climbStairs(n-2)

#  solution 2
def climbStairs(n):
    arr = [1,2]
    if n <= 2:
        return arr[n - 1]
    else:
        # n Greater than 2
        for i in range(2,n):
            arr.append(arr[i - 1] + arr[i - 2])
        return arr[n - 1]

climbStairs(2) # 2
climbStairs(3) # 3