每日一练 | Data Scientist & Business Analyst & Leetcode 面试题 721

Data Application Lab 自2017年6月15日起，每天和你分享讨论一道数据科学(DS)和商业分析(BA) 领域常见的面试问题。

自2017年10月4日起，每天再为大家分享一道Leetcode 算法题。

DS Interview Question

Describe what is a decision tree algorithm.

BA Interview Question

Second Highest Salary

Write a SQL query to get the second highest salary from the Employee table.
+----+--------+
| Id | Salary |
+----+--------+
| 1  | 100    |ta
| 2  | 200    |
| 3  | 300    |
+----+--------+

For example, given the above Employee table, the query should return 200 as the second highest salary. If there is no second highest salary, then the query should return null.

+---------------------+
| SecondHighestSalary |
+---------------------+
| 200                 |
+---------------------+

LeetCode Question

N Queen

Description:

The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.

Input: 4

Output: [[".Q…", // Solution 1 “…Q”, “Q…”, “…Q.”], ["…Q.", // Solution 2 “Q…”, “…Q”, “.Q…”]]

DS Interview Question & Answer

Give me some examples about the applications of Naive Bayes Algorithms.

Real time Prediction: Naive Bayes is an eager learning classifier and it is sure fast. Thus, it could be used for making predictions in real time.

Multi class Prediction: This algorithm is also well known for multi class prediction feature. Here we can predict the probability of multiple classes of target variable.

Text classification/ Spam Filtering/ Sentiment Analysis: Naive Bayes classifiers mostly used in text classification (due to better result in multi class problems and independence rule) have higher success rate as compared to other algorithms. As a result, it is widely used in Spam filtering (identify spam e-mail) and Sentiment Analysis (in social media analysis, to identify positive and negative customer sentiments)

Recommendation System: Naive Bayes Classifier and Collaborative Filtering together builds a Recommendation System that uses machine learning and data mining techniques to filter unseen information and predict whether a user would like a given resource or not

BA Interview Question & Answer

Combine two tables

Table: Person

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| PersonId    | int     |
| FirstName   | varchar |
| LastName    | varchar |
+-------------+---------+

PersonId is the primary key column for this table.

Table: Address
+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| AddressId   | int     |
| PersonId    | int     |
| City        | varchar |
| State       | varchar |
+-------------+---------+

AddressId is the primary key column for this table.

Write a SQL query for a report that provides the following information for each person in the Person table, regardless if there is an address for each of those people:

FirstName, LastName, City, State

Answers: Using outer join. Since the PersonID in table Address is the foreign key of a table Person, we can join this two table to get the address information of a person. Considering there might not be an address information for every person, we should use outer join instead of the default inner join.

MySQL:

select p.FirstName, p.LastName, a.City, a.State

from p.Person

left join a.Address

on p.PersonId = a.PersonId;

Reference:

https://leetcode.com/problems/combine-two-tables/description/