一直很好奇 leetcode 是怎么判断随机算法的正误的 - V2EX
eastphoton

一直很好奇 leetcode 是怎么判断随机算法的正误的

  •  
  •   eastphoton Jun 26, 2022 4811 views
    This topic created in 1416 days ago, the information mentioned may be changed or developed.

    比如今天的每日一题: https://leetcode.cn/problems/random-pick-with-blacklist/, 还有这些: https://leetcode.cn/tag/randomized/problemset/

    毕竟随机结果没法直接对比标准答案,感觉要判断正误就挺麻烦,但 leetcode 可以测出来正确性。

    有时候写出来某个细节差个+1 -1 ,那概率分布也差不太多吧,它也能测出来有错误不给 AC 。 感觉就挺神奇的。

    没有搜到有对这个的讨论。。

    6 replies    2022-06-26 20:16:43 +08:00
    stein42
        1
    stein42  
       Jun 26, 2022   1
    应该是用统计学里的假设检验来验证,这里是离散均匀分布,可以用皮尔森卡方检定。
    假设检验本身就可能犯第一类错误(拒绝正确结果)和第二类错误(接受错误结果)。
    我试过,轻微改变分布还是能通过。

    ```
    import bisect
    import random


    class Solution:
    ....def __init__(self, n: int, blacklist: List[int]):
    ........self.m = n - len(blacklist)
    ........self.ss = [a - i for i, a in enumerate(sorted(blacklist))]

    ....def pick(self) -> int:
    ........r = random.randrange(self.m)
    ........return r + bisect.bisect_right(self.ss, r)
    ```

    ```
    import bisect
    import random


    class Solution:
    ....def __init__(self, n: int, blacklist: List[int]):
    ........self.m = n - len(blacklist)
    ........self.ss = [a - i for i, a in enumerate(sorted(blacklist))]

    ....def pick(self) -> int:
    ........if random.random() < 1 / (100 * self.m):
    ............r = 0
    ........else:
    ............r = random.randrange(self.m)
    ........return r + bisect.bisect_right(self.ss, r)
    ```
    virusdefender
        2/div>
    virusdefender  
       Jun 26, 2022
    special judge 吧,也就是写一段代码来判断,各种 oj 都有这功能
    SingeeKing
        3
    SingeeKing  
    PRO
       Jun 26, 2022 via iPhone
    咱就说,有没有一种可能,他是跑了你的代码然后检查输入输出
    SingeeKing
        4
    SingeeKing  
    PRO
       Jun 26, 2022 via iPhone
    哦不我看错了,忽略我…
    adjusted
        5
    adjusted  
       Jun 26, 2022   1
    random 设置下 seed 吧
    wy315700
        6
    wy315700  
       Jun 26, 2022 via Android
    special judge 写一段代码来检测你的输出的,写 oj 的时候经常用到的,除了随机数算法,一些涉及浮点数的可能也要用到
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