Category Git
Short answers to the question what is the difference between...
Short answers to the question how to revert a git...
Short answers to the question how to modify existing unpushed...
Short answers to the question how to undo a git...
Short answers to the question how to rename a local...
Short answers to the question how to delete a git...
Short answers to the question how to checkout a remote...
Short answers to the question how to undo the most...
Category MySQL
The INNER JOIN keyword selects records that have matching values...
Aliases are nicknames. They give us a shorthand way of...
The OR operator combines two Boolean expressions and returns true...
The LIMIT clause is used in the SELECT statement to...
The LIKE operator is used in a WHERE clause to...
To test whether a value is NULL or not, we...
The IN operator allows us to determine if a specified...
The BETWEEN operator selects values within a given range.
The AND operator is a logical operator that combines two...
The WHERE clause allows us to choose which rows are...
In order to remove duplicate rows, we use the DISTINCT...
The ORDER BY clause is used to sort the result-set...
The SELECT statement allows us to read data from one...
Category Database
LeetCode 1939. Write an SQL query to find the IDs...
LeetCode 1949. Write an SQL query to find all the...
LeetCode 1919. Write an SQL query to report the similar...
LeetCode 1917. Write an SQL query to recommend friends to...
LeetCode 1972. Write an SQL query to report the IDs...
LeetCode 1988. Write an SQL query to report the minimum...
LeetCode 1965. Write an SQL query to report the IDs...
LeetCode 1978. Write an SQL query to report the IDs...
LeetCode 1990. Write an SQL query to report the number...
LeetCode 1907. Write an SQL query to report the number...
LeetCode 1934. Write an SQL query to find the confirmation...
LeetCode 1951. Write an SQL query to find all the...
LeetCode 1890. Write an SQL query to report the latest...
LeetCode 1843. Write an SQL query to report the IDs...
LeetCode 1892. Write an SQL query to find all the...
LeetCode 1867. Write an SQL query to find the order_id...
LeetCode 1831. Write an SQL query to report the IDs...
LeetCode 1841. Write an SQL query to report the statistics...
LeetCode 1875. Write an SQL query to report the IDs...
LeetCode 1821. Write an SQL query to report the customers...
LeetCode 1853. Write an SQL query to convert each date...
LeetCode 1873. Write an SQL query to calculate the bonus...
LeetCode 1795. Write an SQL query to rearrange the Products...
LeetCode 1811. Write an SQL query to report the name...
LeetCode 1809. Write an SQL query to report all the...
LeetCode 1789. Write an SQL query to report all the...
LeetCode 1783. Write an SQL query to report the number...
LeetCode 1777. Write an SQL query to find the price...
LeetCode 1767. Write an SQL query to report the IDs...
LeetCode 1757. Write an SQL query to find the ids...
LeetCode 1747. Write an SQL query to find the account_id...
LeetCode 1741. Write an SQL query to calculate the total...
LeetCode 1731. Write an SQL query to report the ids...
LeetCode 1729. Write an SQL query that will, for each...
LeetCode 1715. Write an SQL query to count the number...
LeetCode 1709. Write an SQL query that will, for each...
LeetCode 1384. Write an SQL query to report the Total...
LeetCode 1479. Write an SQL query to report how many...
LeetCode 1651. Write an SQL query to compute the average_ride_distance...
LeetCode 1369. Write an SQL query to show the second...
LeetCode 1412. Write an SQL query to report the students...
LeetCode 1194. Write an SQL query to find the winner...
LeetCode 618. A U.S graduate school has students from Asia,...
LeetCode 1225. Write an SQL query to generate a report...
LeetCode 569. Write a SQL query to find the median...
LeetCode 1159. Write an SQL query to find for each...
LeetCode 1635. Write an SQL query to report the following...
LeetCode 1097. Write an SQL query that reports for each...
LeetCode 1127. Write an SQL query to find the total...
LeetCode 262. Write a SQL query to find the cancellation...
LeetCode 1336. Write an SQL query to find how many...
LeetCode 601. Write an SQL query to display the records...
LeetCode 1645. Write an SQL query to report the percentage...
LeetCode 571. Write a query to find the median of...
LeetCode 579. Write a SQL to get the cumulative sum...
LeetCode 185. Write a SQL query to find employees who...
LeetCode 615. Given two tables as below, write a query...
LeetCode 1098. Write an SQL query that reports the books...
LeetCode 614. Please write a sql query to get the...
LeetCode 1132. Write an SQL query to find the average...
LeetCode 1699. Write an SQL query to report the number...
LeetCode 177. Write a SQL query to get the nth...
LeetCode 1107. Write an SQL query that reports for every...
LeetCode 1205. Write an SQL query to find for each...
LeetCode 578. Write a sql query to identify the question...
LeetCode 184. Write a SQL query to find employees who...
LeetCode 1149. Write an SQL query to find all the...
LeetCode 1454. Write an SQL query to find the id...
LeetCode 574. Write a sql to find the name of...
LeetCode 1212. Write an SQL query that selects the team_id,...
LeetCode 178. Write a SQL query to rank scores. If...
LeetCode 1070. Write an SQL query that selects the product...
LeetCode 1341. Write the following SQL query to find the...
LeetCode 585. Write a query to print the sum of...
LeetCode 1174. Write an SQL query to find the percentage...
LeetCode 602. In social network like Facebook or Twitter, people...
LeetCode 1501. Write an SQL query to find the countries...
LeetCode 580. A university uses 2 data tables, student and...
LeetCode 1555. Our bank records all transactions in the table...
LeetCode 608. Given a table tree, id is identifier of...
LeetCode 1549. Write an SQL query to find the most...
LeetCode 612. Write a query to find the shortest distance...
LeetCode 1459. Write an SQL query to report of all...
LeetCode 1164. Write an SQL query to find the prices...
LeetCode 1264. Write an SQL query to recommend pages to...
LeetCode 1193. Write an SQL query to find for each...
LeetCode 1158. Write an SQL query to find for each...
LeetCode 570. Given the Employee table, write a SQL query...
LeetCode 1613. Write an SQL query to find the missing...
LeetCode 626. Mary is a teacher in a middle school...
LeetCode 1045. Write an SQL query for a report that...
LeetCode 1126. Write an SQL query to find all active...
LeetCode 1532. Write an SQL query to find the most...
LeetCode 1321. You are the restaurant owner and you want...
LeetCode 1077. Write an SQL query that reports the most...
LeetCode 1364. Write an SQL query to find the following...
LeetCode 1421. Write an SQL query to find the npv...
LeetCode 1204. Write an SQL query to find the person_name...
LeetCode 1112. Write a SQL query to find the highest...
LeetCode 1440. Write an SQL query to evaluate the boolean...
LeetCode 1468. Write an SQL query to find the salaries...
LeetCode 1355. Write an SQL query to find the names...
LeetCode 1142. Write an SQL query to find the average...
LeetCode 1596. Write an SQL query to find the most...
LeetCode 1308. Write an SQL query to find the total...
LeetCode 1495. Write an SQL query to report the distinct...
LeetCode 597. Write an SQL query to find the overall...
LeetCode 1285. Write an SQL query to find the start...
LeetCode 1398. Write an SQL query to report the customer_id...
LeetCode 596. Please list out all classes which have more...
LeetCode 1393. Write an SQL query to report the Capital...
LeetCode 619. Table my_numbers contains many numbers in column num...
LeetCode 1445. Write an SQL query to report the difference...
LeetCode 1270. Write an SQL query to find employee_id of...
LeetCode 1294. Write an SQL query to find the type...
LeetCode 1141. Write an SQL query to find the daily...
LeetCode 610. A pupil Tim gets homework to identify whether...
LeetCode 1280. Write an SQL query to find the number...
LeetCode 607. Given three tables, salesperson, company, orders.
LeetCode 1084. Write an SQL query that reports the products...
LeetCode 1083. Write an SQL query that reports the buyers...
LeetCode 1113. Write an SQL query that reports the number...
LeetCode 1211. Write an SQL query to find each query_name,...
LeetCode 1076. Write an SQL query that reports all the...
LeetCode 1075. Write an SQL query that reports the average...
LeetCode 1241. Write an SQL query to find number of...
LeetCode 620. X city opened a new cinema, many people...
LeetCode 1543. Write an SQL query to report product_name in...
LeetCode 603. Several friends at a cinema ticket office would...
LeetCode 1322. A company is running Ads and wants to...
LeetCode 1407. Write an SQL query to report the distance...
LeetCode 627. Given a table salary, such as the one...
LeetCode 613. Write a query to find the shortest distance...
LeetCode 1082. Write an SQL query that reports the best...
LeetCode 1179. Write an SQL query to reformat the table...
LeetCode 1069. Write an SQL query that reports the total...
LeetCode 1068. Write an SQL query that reports all product...
LeetCode 1327. Write an SQL query to get the names...
LeetCode 1173. Write an SQL query to find the percentage...
LeetCode 1517. Write an SQL query to find the users...
LeetCode 584. Given a table customer holding customers information and...
LeetCode 586. Query the customer_number from the orders table for...
LeetCode 1511. Write an SQL query to report the customer_id...
LeetCode 1435. You want to know how long a user...
LeetCode 595. Write a SQL solution to output big countries’...
LeetCode 1251. Write an SQL query to find the average...
LeetCode 1148. Write an SQL query to find all the...
LeetCode 1050. Write a SQL query for a report that...
LeetCode 1565. Write an SQL query to find the number...
LeetCode 1607. Write an SQL query to report the names...
LeetCode 197. Write an SQL query to find all dates’...
LeetCode 550. Write an SQL query that reports the fraction...
LeetCode 534. Write an SQL query that reports for each...
LeetCode 512. Write a SQL query that reports the device...
LeetCode 511. Write an SQL query that reports the first...
LeetCode 577. Select all employee’s name and bonus whose bonus...
LeetCode 196. Write a SQL query to delete all duplicate...
LeetCode 1693. Write an SQL query that will, for each...
LeetCode 1581. Write an SQL query to find the IDs...
LeetCode 1677. Write an SQL query that will, for all...
LeetCode 1633. Write an SQL query to find the percentage...
LeetCode 1667. Write an SQL query to fix the names...
LeetCode 182. Write a SQL query to find all duplicate...
LeetCode 183. Write a SQL query to find all customers...
LeetCode 180. Write an SQL query to find all numbers...
LeetCode 1661. There is a factory website that has several...
LeetCode 176. Given the Employee table, write a SQL query...
LeetCode 181. Given the Employee table, write a SQL query...
LeetCode 1587. Write an SQL query to report the name...
LeetCode 1484. Write an SQL query to find for each...
LeetCode 1623. Write an SQL query to find all the...
LeetCode 1571. Write an SQL query to report how much...
LeetCode 1350. Write an SQL query to find the id...
LeetCode 1378. Write an SQL query to show the unique...
LeetCode 1527. Write an SQL query to report the patient_id,...
LeetCode 1683. Write an SQL query to find the IDs...
LeetCode 1303. Write an SQL query to find the team...
LeetCode 175. Write a SQL query for a report that...
Category List
A growing list of Git questions and short answers.
A growing list of MySQL tutorials.
A list of LeetCode database problems and solutions.
A growing list of LeetCode problems and solutions.
A growing list of posts under the topic of Operating...
A growing list of posts under the topic of Object...
A growing list of posts under the topic of C++...
Category Operating System
Another important question is how threads interact when they access...
A thread is an abstraction for a single running process....
How can the OS provide the illusion of nearly-endless supply...
How can the OS decide which page(s) to evict from...
How can the OS make use of a larger, slower...
How can we make page tables smaller.
How can we speed up address translation, and generally avoid...
How can we virtualize memory with pages, so as to...
How to support a large address space with (potentially) a...
How can we relocate the process in memory in a...
Virtual Memory is an abstraction that the Operating System provides...
Category Object-Oriented Design
Design the data structures for an online book reader system...
Design a parking lot using object-oriented principles. We will focus...
An object oriented design problem. Imagine you have a call...
Category Design Pattern
The singleton design pattern is a type of creational pattern...
The factory design pattern is a type of creational pattern...
Category C++ Concepts
Every C++ expression has a type and belongs to a...
Perfect forwarding reduces the need for overloaded functions and helps...
The rvalue references enable us to distinguish an lvalue from...
A reference is an alias of another object. It stores...
An lvalue reference is another name of an object. An...
A lambda expression is a convenient way of defining an...
A template specialization is a separate definition in which the...
C++ transforms the operands to a common type before performing...
An explicit conversion is also called as a cast. There...
The constructor that takes a single parameter that is a...
A function specified as inline is expanded everywhere it is...
A function pointer is a pointer that denotes a function...
Sometimes an object must store a way to access the...
A friend class can access private and protected members of...
A unique_ptr does not share its pointer. It cannot be...
In modern C++ programming, the Standard Library includes smart pointers,...
The shared_ptr type is a smart pointer that is designed...
A template is a blueprint or formula for creating a...
Polymorphism means having more than one function with the same...
An interface describes the behavior or capabilities of a C++...
Category Data Structure
LeetCode 127. Given two words, beginWord and endWord, and a...
LeetCode 126. Given two words, beginWord and endWord, and a...
LeetCode 125. A phrase is a palindrome if, after converting...
LeetCode 120. Given a triangle array, return the minimum path...
LeetCode 130. Given an m x n matrix board containing...
LeetCode 129. You are given the root of a binary...
LeetCode 116. You are given a perfect binary tree where...
LeetCode 117. Given a binary tree, populate each next pointer...
LeetCode 112. Given the root of a binary tree and...
LeetCode 113. Given the root of a binary tree and...
LeetCode 118. Given an integer numRows, return the first numRows...
LeetCode 119. Given an integer rowIndex, return the rowIndex^th (0-indexed)...
LeetCode 111. Given a binary tree, find its minimum depth....
LeetCode 128. Given an unsorted array of integers nums, return...
LeetCode 114. Given the root of a binary tree, flatten...
LeetCode 115. Given two strings s and t, return the...
LeetCode 109. Given the head of a singly linked list...
LeetCode 124. A path in a binary tree is a...
LeetCode 121. You are given an array prices where prices[i]...
LeetCode 123. You are given an array prices where prices[i]...
LeetCode 122. You are given an integer array prices where...
LeetCode 110. Given a binary tree, determine if it is...
LeetCode 101. Given the root of a binary tree, check...
LeetCode 104. Given the root of a binary tree, return...
LeetCode 108. Given an integer array nums where the elements...
LeetCode 105. Given two integer arrays preorder and inorder where...
LeetCode 106. Given two integer arrays inorder and postorder where...
LeetCode 103. Given the root of a binary tree, return...
LeetCode 102. Given the root of a binary tree, return...
LeetCode 107. Given the root of a binary tree, return...
LeetCode 98. Given the root of a binary tree, determine...
LeetCode 100. Given the roots of two binary trees p...
LeetCode 99. You are given the root of a binary...
LeetCode 83. Given the head of a sorted linked list,...
LeetCode 82. Given the head of a sorted linked list,...
LeetCode 94. Given an m x n grid of characters...
LeetCode 75. Given an array nums with n objects colored...
LeetCode 71. Given a string path, which is an absolute...
LeetCode 73. Given an m x n integer matrix matrix,...
LeetCode 76. Given two strings s and t of lengths...
LeetCode 72. Given two strings word1 and word2, return the...
LeetCode 77. Given two integers n and k, return all...
LeetCode 65. Given a string s, return true if s...
LeetCode 62. A robot is located at the top-left corner...
LeetCode 63. A robot is located at the top-left corner...
LeetCode 68. Given an array of strings words and a...
LeetCode 61. Given the head of a linked list, rotate...
LeetCode 66. You are given a large integer represented as...
LeetCode 64. Given a m x n grid filled with...
LeetCode 70. You are climbing a staircase. It takes n...
LeetCode 67. A robot is located at the top-left corner...
LeetCode 54. Given an m x n matrix, return all...
LeetCode 59. Given a positive integer n, generate an n...
LeetCode 58. Given a string s consisting of some words...
LeetCode 57. Insert newInterval into intervals such that intervals is...
LeetCode 6. Write the code that will take a string...
LeetCode 36. Determine if a 9 x 9 Sudoku board...
LeetCode 42. Given n non-negative integers representing an elevation map...
LeetCode 30. You are given a string s and an...
LeetCode 33. Given the array nums after the possible rotation...
LeetCode 48. Determine if a 9 x 9 Sudoku board...
LeetCode 25. Given a linked list, reverse the nodes of...
LeetCode 27. Given an integer array nums and an integer...
LeetCode 9. Given an integer x, return true if x...
LeetCode 31. Implement next permutation, which rearranges numbers into the...
LeetCode 43. Given two non-negative integers num1 and num2 represented...
LeetCode 32. Given a string containing just the characters ‘(‘...
LeetCode 45. Given an array of non-negative integers nums, you...
LeetCode 12. Given an integer, convert it to a roman...
LeetCode 28. Implement strStr().
LeetCode 49. Given an array of strings strs, group the...
LeetCode 29. Write the code that will take a string...
LeetCode 38. Write the code that will take a string...
LeetCode 16. Given an integer array nums of length n...
LeetCode 20. Given a string s containing just the characters...
LeetCode 24. Given a linked list, swap every two adjacent...
LeetCode 19. Given the head of a linked list, remove...
LeetCode 26. Given an integer array nums sorted in non-decreasing...
LeetCode 14. Write a function to find the longest common...
LeetCode 22. Given n pairs of parentheses, write a function...
LeetCode 1902. You are given a 0-indexed integer array order...
LeetCode 1999. Given three integers, k, digit1, and digit2, you...
LeetCode 2000. Given a 0-indexed string word and a character...
LeetCode 1812. You are given coordinates, a string that represents...
LeetCode 8. Implement the myAtoi(string s) function, which converts a...
LeetCode 3. Given a string s, find the length of...
LeetCode 2. You are given two non-empty linked lists representing...
LeetCode 1748. You are given an integer array nums. The...
LeetCode 380. Implement a RandomizedSet class.
LeetCode 961. In a array A of size 2N, there...
LeetCode 349. Given two arrays, write a function to compute...
LeetCode 1213. Given three integer arrays arr1, arr2 and arr3...
LeetCode 771. You’re given strings jewels representing the types of...
LeetCode 1512. Given an array of integers nums. Return the...
LeetCode 1539. Given an array arr of positive integers sorted...
LeetCode 1224. Given an array nums of positive integers, return...
LeetCode 206. Reverse a singly linked list.
LeetCode 92. Reverse a linked list from position m to...
LeetCode 234. Given a singly linked list, determine if it’s...
LeetCode 23. You are given an array of k linked-lists...
LeetCode 21. Merge two sorted linked lists and return a...
LeetCode 1032. Implement the StreamChecker class as follows. Constructor, initialize...
LeetCode 421. Given an integer array nums, return the maximum...
LeetCode 208. Implement a Trie with insert, search, and startsWith...
LeetCode 1023. A query word matches a given pattern if...
LeetCode 212. Given an m x n board of characters...
LeetCode 648. Given a dictionary consisting of many roots, and...
LeetCode 720. Given a list of strings words representing an...
LeetCode 472. Given a list of words (without duplicates), return...
Category Algorithm
LeetCode 127. Given two words, beginWord and endWord, and a...
LeetCode 126. Given two words, beginWord and endWord, and a...
LeetCode 125. A phrase is a palindrome if, after converting...
LeetCode 120. Given a triangle array, return the minimum path...
LeetCode 130. Given an m x n matrix board containing...
LeetCode 129. You are given the root of a binary...
LeetCode 116. You are given a perfect binary tree where...
LeetCode 117. Given a binary tree, populate each next pointer...
LeetCode 112. Given the root of a binary tree and...
LeetCode 113. Given the root of a binary tree and...
LeetCode 118. Given an integer numRows, return the first numRows...
LeetCode 119. Given an integer rowIndex, return the rowIndex^th (0-indexed)...
LeetCode 111. Given a binary tree, find its minimum depth....
LeetCode 128. Given an unsorted array of integers nums, return...
LeetCode 114. Given the root of a binary tree, flatten...
LeetCode 115. Given two strings s and t, return the...
LeetCode 109. Given the head of a singly linked list...
LeetCode 124. A path in a binary tree is a...
LeetCode 121. You are given an array prices where prices[i]...
LeetCode 123. You are given an array prices where prices[i]...
LeetCode 122. You are given an integer array prices where...
LeetCode 110. Given a binary tree, determine if it is...
LeetCode 97. Given strings s1, s2, and s3, find whether...
LeetCode 79. Given an m x n grid of characters...
LeetCode 96. Given an integer n, return the number of...
LeetCode 95. Given an integer n, return all the structurally...
LeetCode 78. Given an integer array nums of unique elements,...
LeetCode 90. Given an integer array nums that may contain...
LeetCode 81. There is an integer array nums sorted in...
LeetCode 87. Given two strings s1 and s2 of the...
LeetCode 93. Given a string s containing only digits, return...
LeetCode 80. Given an integer array nums sorted in non-decreasing...
LeetCode 86. Given the head of a linked list and...
LeetCode 88. You are given two integer arrays nums1 and...
LeetCode 85. Given a rows x cols binary matrix filled...
LeetCode 84. Given an array of integers heights representing the...
LeetCode 89. Given an integer n, return any valid n-bit...
LeetCode 91. Given a string s containing only digits, return...
LeetCode 74. Write an efficient algorithm that searches for a...
LeetCode 60. Given n and k, return the kth permutation...
LeetCode 51. Given an integer n, return all distinct solutions...
LeetCode 52. Given an integer n, return the number of...
LeetCode 53. Given an integer array nums, find the contiguous...
LeetCode 55. Given an m x n matrix, return all...
LeetCode 44. Write the code that will take a string...
LeetCode 37. Write a program to solve a Sudoku puzzle...
LeetCode 10. Given an input string s and a pattern...
LeetCode 50. Determine if a 9 x 9 Sudoku board...
LeetCode 46. Given an array nums of distinct integers, return...
LeetCode 47. Given a collection of numbers, nums, that might...
LeetCode 41. Given an unsorted integer array nums, return the...
LeetCode 34. Given the array nums after the possible rotation...
LeetCode 39. Given an array of distinct integers candidates and...
LeetCode 40. Given a collection of candidate numbers (candidates) and...
LeetCode 13. Given a roman numeral, convert it to an...
LeetCode 7. Given a signed 32-bit integer x, return x...
LeetCode 5. Given a string s, return the longest palindromic...
LeetCode 17. Given a string containing digits from 2-9 inclusive,...
LeetCode 11. Given n non-negative integers a_1, a_2, …, a_n...
LeetCode 200. Given an m x n 2d grid map...
LeetCode 56. Given an array of intervals, merge all overlapping...
LeetCode 1438. Given an array of integers nums and an...
LeetCode 543. Given a binary tree, compute the diameter of...
LeetCode 4. Given two sorted arrays nums1 and nums2 of...
LeetCode 367. Given a positive integer num, write a function...
LeetCode 69. Given a non-negative integer x, compute and return...
LeetCode 35. Given a sorted array of distinct integers and...
LeetCode 167. Given an array of integers nums sorted in...
LeetCode 974. Given an array of integers nums and an...
LeetCode 454. Given four lists A, B, C, D of...
LeetCode 523. Given an array of non-negative integers nums and...
LeetCode 1099. Given an array of integers nums and an...
LeetCode 560. Given an array of integers nums and an...
LeetCode 713. Given an array of positive integers nums and...
LeetCode 15. Given an array of integers nums, return all...
LeetCode 18. Given an array of integers nums and an...
LeetCode 1. Given an array of integers nums and an...
Category Tutorial
In this post, I will show how I write an...