小黑代码

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        # 数组长度
        n = len(prices)
        # 最大利润
        profit = 0
        # 中间变量
        min_ = prices[0]
        # 遍历每一个数据作为买点
        for i in range(1, n):
            # 滚动获取最小值
            if prices[i] - min_ > profit:
                profit = prices[i] - min_
            if prices[i] < min_:
                min_ = prices[i]
        return profit

在这里插入图片描述

数据库练习

584. 寻找用户推荐人

小黑代码

# Write your MySQL query statement below
SELECT
    name
FROM
    Customer
WHERE
    referee_id != '2' OR referee_id IS NULL

pandas练习

176. 第二高的薪水

小黑代码

import pandas as pd

def second_highest_salary(employee: pd.DataFrame) -> pd.DataFrame:
    data = employee['salary'].tolist()
    data = set(data)
    if len(data) >= 2:
        target = sorted(data)[-2]
        return pd.DataFrame(data=[[target]], columns=['SecondHighestSalary'])
    return pd.DataFrame(data=[[None]], columns=['SecondHighestSalary'])

import pandas as pd

def second_highest_salary(employee: pd.DataFrame) -> pd.DataFrame:
    # 删除重复数据
    salary = employee[['salary']].drop_duplicates(['salary'])
    # 少于两个的返回
    if len(salary) < 2:
        return pd.DataFrame({'SecondHighestSalary':[np.NaN]})
    # 降序排列
    salary = salary.sort_values('salary', ascending=False)
    # 重命名
    salary.rename({'salary': 'SecondHighestSalary'}, axis=1, inplace=True)
    # 返回
    return salary.head(2).tail(1)

多线程练习

1114. 按序打印

使用 synchronization

from threading import Lock
class Foo:
    def __init__(self):
        # 初始化锁
        self.firstDone = Lock()
        self.secondDone = Lock()
        # 申请锁
        self.firstDone.acquire()
        self.secondDone.acquire()

    def first(self, printFirst: 'Callable[[], None]') -> None:
        
        # printFirst() outputs "first". Do not change or remove this line.
        printFirst()
        # 释放锁
        self.firstDone.release()



    def second(self, printSecond: 'Callable[[], None]') -> None:
        with self.firstDone:
            # printSecond() outputs "second". Do not change or remove this line.
            printSecond()
            self.secondDone.release()


    def third(self, printThird: 'Callable[[], None]') -> None:
        with self.secondDone:
            # printThird() outputs "third". Do not change or remove this line.
            printThird()