每日一练 | Data Scientist Business Analyst Leetcode 面试题 1200

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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。

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DS Interview Question

What is the difference between stochastic gradient descent (SGD) and gradient descent (GD)?

BA Interview Question

Write a query in SQL to obtain the name of the physicians who are trained for a special treatment.

Sample table: physician

Employeeid | name | position | ssn
------------+------------------------------+-------------------------------------------+---------------------
1 | John Dorian | Staff Internist | 111111111
2 | Elliot Reid | Attending Physician | 222222222
3 | Christopher Turk | Surgical Attending Physician | 333333333
4 | Percival Cox | Senior Attending Physician | 444444444
5 | Bob Kelso | Head Chief of Medicine | 555555555
6 | Todd Quinlan | Surgical Attenian | 666666666
7 | John Wen | Surgical Attending Physician | 777777777
8 | Keith Dudemeister | MD Resident | 888888888
9 | Molly Clock | Attending Psychiatrist | 999999999

Sample table: procedure

code | name | cost
------+-------------------------------------------+-------------
1 | Reverse Rhinopodoplasty | 1500
2 | Obtuse Pyloric Recombobulation | 3750
3 | Folded Demiophtalmectomy | 4500
4 | Complete Walletectomy | 10000
5 | Obfuscated Dermogastrotomy | 4899
6 | Reversible Pancreomyoplasty | 5600
7 | Follicular Demiectomy | 25

LeetCode Question

Add Two Linked Lists

Description:

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

DSInterview Question & Answer

While working on a data set, how do you select important variables? Explain your methods.

• Remove the correlated variables prior to selecting important variables

• Use linear regression and select variables based on p values

• Use Forward Selection, Backward Selection, Stepwise Selection

• Use Random Forest, Xgboost and plot variable importance chart

• Measure information gain for the available set of features and select top n features accordingly.

• …

BA Interview Question & Answer

Write a query in SQL to count the number of unavailable rooms

Sample table: room

roomnumber | roomtype | blockfloor | blockcode | unavailable
-----------+----------+------------+-----------+-------------
101 | Single | 1 | 1 | f
102 | Single | 1 | 1 | f
103 | Single | 1 | 1 | f
111 | Single | 1 | 2 | f
112 | Single | 1 | 2 | t
113 | Single | 1 | 2 | f
121 | Single | 1 | 3 | f
122 | Single | 1 | 3 | f
123 | Single | 1 | 3 | f
201 | Single | 2 | 1 |
202 | Single | 2 | 1 | f
203 | Single | 2 | 1 | f
211 | Single | 2 | 2 | f

212 | Single | 2 | 2 | f
213 | Single | 2 | 2 | t
221 | Single | 2 | 3 | f
222 | Single | 2 | 3 | f
223 | Single | 2 | 3 | f
301 | Single | 3 | 1 | f
302 | Single | 3 | 1 | t
303 | Single | 3 | 1 | f
311 | Single | 3 | 2 | f
312 | Single | 3 | 2 | f
313 | Single | 3 | 2 | f
321 | Single | 3 | 3 | t
322 | Single | 3 | 3 | f
323 | Single | 3 | 3 | f
401 | Single | 4 | 1 | f
402 | Single | 4 | 1 | t
403 | Single | 4 | 1 | f
411 | Single | 4 | 2 | f
412 | Single | 4 | 2 | f
413 | Single | 4 | 2 | f
421 | Single | 4 | 3 | t
422 | Single | 4 | 3 | f
423 | Single | 4 | 3 | f

Answer:

7

SELECT count(*) "Number of available rooms"
FROM room
WHERE unavailable='t'

LeetCode Question & Answer

Rotate List

Description:

Given a list, rotate the list to the right by k places, where k is non-negative.

Input: 1->2->3->4->5->NULL k=2

Output: 4->5->1->2->3->NULL

Tips:

注意所有corner case

Code:

时间复杂度：O(n)

空间复杂度：O(1)