在Python中没有定义全局名称助手，即使存在函数

Question

我正在处理这个问题https://leetcode.com/problems/climbing-stairs，得到一个错误“global name helper is not defined”。但它是在类中定义的？你知道吗

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

        return helper(0, n)

    def helper(self, curr, n):
        if (curr > n):
            return 0

        if (curr == n):
            return 1

        return helper(curr + 1, n) + helper(curr + 2, n)

Answer 1

helper是Solution实例的绑定函数，需要在self上调用它。你知道吗

根据较大输入上的超时错误，这是因为每次调用helper都要进行2次递归调用，这意味着运行时复杂性为O(2^N)。你知道吗

因为许多调用都具有相同的参数，所以可以使用^{}缓存以前调用的结果，从而将其减少到O(N)

from functools import lru_cache

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

        return self.helper(0, n)

    @lru_cache()
    def helper(self, curr, n):
        if (curr > n):
            return 0

        if (curr == n):
            return 1

        return self.helper(curr + 1, n) + self.helper(curr + 2, n)


s = Solution()
print(s.climbStairs(35))

Answer 2

您缺少helper的'self'参数，即将helper（）替换为自助服务（）应该是可行的。你知道吗

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

        return self.helper(0, n)

    def helper(self, curr, n):
        if (curr > n):
            return 0

        if (curr == n):
            return 1

        return self.helper(curr + 1, n) + self.helper(curr + 2, n)