每日一练 | Data Scientist & Business Analyst & Leetcode 面试题 326
自2017年6月15日起，数据应用学院与你一起温习数据科学（DS）和商业分析（BA）领域常见的面试问题。从2017年10月4号起，每天再为大家分享一道Leetcode算法题。
希望积极寻求相关领域工作的你每天关注我们的问题并且与我们一起思考，我们将会在第二天给出答案。
Day 226
DS Interview Questions
What is the difference between stochastic gradient descent (SGD) and gradient descent (GD)?
BA Interview Questions
R Programming: What are six types of atomic vector?
LeetCode Questions
The count-and-say sequence is the sequence of integers with the first five terms as following:
1 is read off as “one 1” or 11.
11 is read off as “two 1s” or 21.
21 is read off as “one 2, then one 1” or 1211.
Given an integer n, generate the nth term of the count-and-say sequence.
Note: Each term of the sequence of integers will be represented as a string.
Description:
Input: 4
Output: “1211”
欲知答案如何？请见下期分解！
Day 225 答案揭晓
DS Interview Questions
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 Questions
What is CPI in the mobile gaming industry?
The CPI is how much we spend on advertising to acquire a consumer for downloading and installing a mobile game app, which is a indicator on whether or nor it make sense to invest in mobile game app install advertisements and other customer acquisition campaigns.
If it cost less, which implies your customer would generate amount of revenue; if it cost high, which suggests marketers should get a new way to increase retention, ARPU(Average Revenue Per User), and referrals from existing customers
LeetCode Questions
Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.
The Sudoku board could be partially filled, where empty cells are filled with the character ‘.’.
A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.
Description:
Assumptions:
Time Complexity: O(n ^ 2)
Space Complexity: O(n ^ 2)
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