Reported Posts II

Table: Actions +---------------+---------+ | Column Name | Type | +---------------+---------+ | user_id | int | | post_id | int | | action_date | date | | action | enum | | extra | varchar | +---------------+---------+ There is no primary key for this table, it may have duplicate rows. The action column is an ENUM type of ('view', 'like', 'reaction', 'comment', 'report', 'share'). The extra column has optional information about the action such as a reason for report or a type of reaction.

by lek tin in "database" access_time 3-min read

Reported Posts

Table: Actions +---------------+---------+ | Column Name | Type | +---------------+---------+ | user_id | int | | post_id | int | | action_date | date | | action | enum | | extra | varchar | +---------------+---------+ There is no primary key for this table, it may have duplicate rows. The action column is an ENUM type of ('view', 'like', 'reaction', 'comment', 'report', 'share'). The extra column has optional information about the action such as a reason for report or a type of reaction.

by lek tin in "database" access_time 2-min read

Max Points on a Line

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line. Example 1 Input: [[1,1],[2,2],[3,3]] Output: 3 Explanation: ^ | | o | o | o +-------------> 0 1 2 3 4 Example 2 Input: [[1,1],[3,2],[5,3],[4,1],[2,3],[1,4]] Output: 4 Explanation: ^ | | o | o o | o | o o +-------------------> 0 1 2 3 4 5 6 NOTE: input types have been changed on April 15, 2019.

by lek tin in "algorithm" access_time 2-min read

Nth Highest Salary

Write a SQL query to get the nth highest salary from the Employee table. +----+--------+ | Id | Salary | +----+--------+ | 1 | 100 | | 2 | 200 | | 3 | 300 | +----+--------+ For example, given the above Employee table, the nth highest salary where n = 2 is 200. If there is no nth highest salary, then the query should return null. +------------------------+ | getNthHighestSalary(2) | +------------------------+ | 200 | +------------------------+ Solution CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT BEGIN DECLARE M INT; SET M = N - 1; RETURN ( SELECT IFNULL( ( SELECT DISTINCT Salary FROM Employee ORDER BY Salary Desc LIMIT 1 OFFSET M ), NULL ) ); END

by lek tin in "database" access_time 1-min read

Reformat Department Table

Table: Department +---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | revenue | int | | month | varchar | +---------------+---------+ (id, month) is the primary key of this table. The table has information about the revenue of each department per month. The month has values in ["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"]. Write an SQL query to reformat the table such that there is a department id column and a revenue column for each month.

by lek tin in "database" access_time 2-min read

Big Countries

There is a table World +-----------------+------------+------------+--------------+---------------+ | name | continent | area | population | gdp | +-----------------+------------+------------+--------------+---------------+ | Afghanistan | Asia | 652230 | 25500100 | 20343000 | | Albania | Europe | 28748 | 2831741 | 12960000 | | Algeria | Africa | 2381741 | 37100000 | 188681000 | | Andorra | Europe | 468 | 78115 | 3712000 | | Angola | Africa | 1246700 | 20609294 | 100990000 | +-----------------+------------+------------+--------------+---------------+ A country is big if it has an area of bigger than 3 million square km or a population of more than 25 million.

by lek tin in "database" access_time 1-min read

Longest Increasing Path in a Matrix

Given an integer matrix, find the length of the longest increasing path. From each cell, you can either move to four directions: left, right, up or down. You may NOT move diagonally or move outside of the boundary (i.e. wrap-around is not allowed). Example 1 Input: nums = [ [9,9,4], [6,6,8], [2,1,1] ] Output: 4 Explanation: The longest increasing path is [1, 2, 6, 9]. Example 2 Input: nums = [ [3,4,5], [3,2,6], [2,2,1] ] Output: 4 Explanation: The longest increasing path is [3, 4, 5, 6].

by lek tin in "algorithm" access_time 2-min read

Fizz Buzz Multithreaded

Write a program that outputs the string representation of numbers from 1 to n, however: If the number is divisible by 3, output "fizz". If the number is divisible by 5, output "buzz". If the number is divisible by both 3 and 5, output "fizzbuzz". For example, for n = 15, we output: 1, 2, fizz, 4, buzz, fizz, 7, 8, fizz, buzz, 11, fizz, 13, 14, fizzbuzz.

by lek tin in "algorithm" access_time 3-min read

Print in Order

Suppose we have a class: public class Foo { public void first() { print("first"); } public void second() { print("second"); } public void third() { print("third"); } } The same instance of Foo will be passed to three different threads. Thread A will call first(), thread B will call second(), and thread C will call third(). Design a mechanism and modify the program to ensure that second() is executed after first(), and third() is executed after second().

by lek tin in "algorithm" access_time 2-min read

The Dining Philosophers

Five silent philosophers sit at a round table with bowls of spaghetti. Forks are placed between each pair of adjacent philosophers. Each philosopher must alternately think and eat. However, a philosopher can only eat spaghetti when they have both left and right forks. Each fork can be held by only one philosopher and so a philosopher can use the fork only if it is not being used by another philosopher. After an individual philosopher finishes eating, they need to put down both forks so that the forks become available to others.

by lek tin in "algorithm" access_time 3-min read