每日一练 | Data Scientist & Business Analyst 面试题 178

大数据应用 · 公众号 · 大数据 · 2017-09-03 09:12

正文

从6月15日起，数据应用学院将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。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 78

DS Interview Questions

Develop a K Nearest Neighbors algorithm from scratch (algorithm coding)

BA Interview Questions

What is CPI in the mobile gaming industry?

欲知答案如何？请见下期分解！

Day 77 答案揭晓

DS Interview Questions

How does the Linear Regression algorithm figure out what are the best coefficient values? (This was a question asked in C3 Energy’s Data Scientist interview)

At the highest level, the coefficients are a function of minimizing the sum of square of the residuals. Next, write down these equations while paying careful attention to what is a residual. To go further, consider the following:

1. Write the minimization goal (ideally in linear algebraic (matrix) notation) of minimizing the sum of squares of the residuals given a linear regression model.

2. Solve the minimization equation by illustrating that the sum of square of the residuals is a convex function, which can be differentiated and the coefficients can be derived by setting the differentiation to 0 and solving that equation.

3. Describe that the complexity of solving the linear algebra based solution in #2 is of polynomial time and a more common solution is by observing that the equation is convex and hence numerical algorithms such as gradient descent may be much more efficient.

BA Interview Questions

Why do you think LTV and ‘cost per install’ (CPI) are important in the mobile gaming industry?

LTV is the revenue we can get from a customer in their lifetime; besides,

we can get 3 important information from LTV, which are crucial to successful mobile gaming marketing:

Monetization: How much customers could spend to your mobile game revenue

Virality: The sum value of new users that a customer will refer to your mobile game

Retention: The length of the average customer lifecycle.