Force buckle - 70 climb stairs

To get to the current staircase , It can be downloaded from n-1 and n-2 When the stairs get

First , Define the initial state

then , Recursion of previous state

Last , Leave the rest to the code

Overtime

class Solution(object):
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        memo = [-1] * (n+1)
        if n <= 2:
            return n
        if memo[n] != -1:
            return memo[n]
        memo[n] = self.climbStairs(n - 1) + self.climbStairs(n - 2)
        return memo[n]

No timeout ： Consider not using functions , Direct value storage

class Solution(object):
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """

        if n <= 2:
            return n
        dp_2 = 1  #  It means dp-2
        dp_1 = 2
        for i in range(3, n + 1):
            res = dp_2 + dp_1
            dp_2 = dp_1
            dp_1 = res
            i = i + 1
        return dp_1