每日一练 | Data Scientist & Business Analyst & Leetcode 面试题 320

Day 220

What are feature vectors?

SQL: Query the Name of any student in STUDENTS who scored higher than  Marks. Order your output by the last three characters of each name. If two or more students both have names ending in the same last three characters (i.e.: Bobby, Robby, etc.), secondary sort them by ascending ID.

The STUDENTS table is described as follows:

The Name column only contains uppercase (A-Z) and lowercase (a-z) letters.

Sample Input:

Sample Output:

Ashley
Julia
Belvet

• Description:

• Given two integers n and k, return all possible combinations of k numbers out of 1 … n.

• Input: n = 4 and k = 2

• Output: [[2,4],[3,4],[2,3],[1,2],[1,3],[1,4],]

Day 219 答案揭晓

What’s the “kernel trick” and how is it useful?

Kernel trick:

Kernel functions can enable in higher-dimension spaces without explicitly calculating the coordinates of points within that dimension: instead, kernel functions compute the inner products between the images of all pairs of data in a feature space.

Why it is useful:

It can calculate the coordinates of higher dimensions while being computationally cheaper than the explicit calculation of said coordinates. Many algorithms can be expressed in terms of inner products. Using the kernel trick enables us effectively run  algorithms in a high-dimensional space with lower-dimensional data.

SQL: Write a query that prints a list of employee names (i.e.: the name attribute) for employees in Employee having a salary greater than  per month who have been employees for less than  months. Sort your result by ascending employee_id.

Sample Output：

Angela
Michael
Todd
Joe

Answer:

select name

from Employee

where months < 10 and salary > 2000

order by employee_id;

Description:

Given a set of distinct integers, nums, return all possible subsets.

Input: [1,2,3]