leetcode brush stairs title -70-

Problem Description

Suppose you are climbing stairs. Need n order to reach your roof.

Every time you can climb one or two steps. How many different ways can climb to the roof of it?

Note: Given n is a positive integer.

Examples

Example 1:

Input: 2
Output: 2
explanation: There are two methods can climb the roof.

1. 1 + 1-order-order
2. Step 2
   Example 2:

Input: 3
Output: 3
Explanation: There are three methods can climb to the roof.

1. Step 1 + 1 + 1-order-order
2. 2 + 1-order-order
3. 2 + 1-order-order

achieve

Dynamic Programming

When n is greater than or equal to 2, the method reaches step number of types of n-th order of f (n-1) + f (n-2)

def climb_stair(n):
    """
    动态规划方法，easy级别
    """
    # 开数组
    step = list(0 for _ in range(n+1))
    step[1] = 1
    step[2] = 2

    if n == 1:
        return 1

    for i in range(3, n+1):
        step[i] = step[i-1] + step[i-2]

    return step[n]

Time complexity of O (n)

Space complexity O (n)