silva
/
ctci
mirror of https://github.com/viniciusfdasilva/ctci.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

chapters 12-15, theory done

This commit is contained in:
anebz 2020-10-19 14:16:31 +02:00
parent d68be1ed2f
commit 8bc5728d9f
5 changed files with 338 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

84
12. C++/README.md Normal file
View File

@ -0,0 +1,84 @@
# 12. C++
## Classes and inheritance
```cpp
#include <iostream>
using namespace std;
// Base class
class Shape {
public:
void setWidth(int w) {
width = w;
}
void setHeight(int h) {
height = h;
}
protected:
int width;
int height;
};
// Derived class
class Rectangle: public Shape {
public:
int getArea() {
return (width * height);
}
};
int main(void) {
Rectangle Rect;
Rect.setWidth(5);
Rect.setHeight(7);
// Print the area of the object.
cout << "Total area: " << Rect.getArea() << endl;
return 0;
}
```
## Constructors and destructors
```cpp
// constructor
Person(int w, h) {
height = h;
width = w;
}
// destructor
~Person() {
delete height;
delete width;
}
```
## Virtual functions
Setting a parent class function in the children class, inheritance.
## Pointers and reference
```cpp
// pointers
int* p = new int;
*p = 7;
int* q = p;
*q = 8
cout << *q; // prints 8
// references
int a = 5;
int& b = a;
b = 7;
cout << a; // prints 7
// pointer arithmetic
int* p = new int[2];
p[0] = 0;
p[1] = 1;
p++;
cout << *p; // prints 1
```

38
13. Java/README.md Normal file
View File

@ -0,0 +1,38 @@
# 13. Java
## Overloading vs. overriding
* Overloading: two methods have the same name, but differ in the type or number of alignments.
* Overriding: a method shares the same name and function signature as another method in its super class
## Collection framework
* ArrayList: dynamically resizing array, growing as you insert elements
* Vector: similar to ArrayList, but synchronized
* LinkedList
* HashMap
```java
ArrayList<String> myArr = new ArrayList<String>();
myArr.add("one");
myArr.add("two");
System.out.println(myArr.get(0));
Vector<String> myVec = new Vector<String>();
myVec.add("one");
myVec.add("two");
System.out.println(myVec.get(0));
LinkedList<String> myLinkedList = new LinkedList<String>();
myLinkedList.add("two");
myLinkedList.addFirst("one");
Iterator<String> iter = myLinkedList.iterator();
while (iter.hasNext()) {
System.out.println(iter.next());
}
HashMap<String, String> map = new HashMap<String, String>();
map.put("one", "uno");
map.put("two", "dos");
System.out.println(map.get("one"));
```

44
14. Databases/14.1. Multiple apartments.md Normal file
View File

@ -0,0 +1,44 @@
# 14.1. Multiple apartments
> Write a SQL query to get a list of tenants who are renting more than one apartment
| Apartments | |
|-|-|
| AptID | int |
| UnitNumber | varchar(10) |
| BuildingID | int |
| Buildings | |
|-|-|
| BuildingID | int |
| ComplexID | int |
| BuildingName | varchar(100) |
| Address | varchar(500) |
| Requests | |
|-|-|
| RequestID | int |
| Status | varchar(100) |
| AptID | int |
| Description | varchar(500) |
| Complexes | |
|-|-|
| ComplexID | int |
| ComplexName | varchar(100) |
| AptTenants | |
|-|-|
| TenantID | int |
| AptId | int |
| Tenants | |
|-|-|
| TenantID | int |
| TenantName | varchar(100) |
```sql
SELECT TenantName FROM Tenants
INNER JOIN (SELECT TenantID FROM AptTenants GROUP BY TenantID HAVING count(*) > 1) C
ON Tenants.TenantID == C.TenantID
```

58
14. Databases/README.md Normal file
View File

@ -0,0 +1,58 @@
# 14. Databases
```sql
SELECT CourseName, TeacherName FROM Courses, Teachers WHERE Courses.TeacherID = Teachers.TeacherID
```
Normalized databases are designed to minimize redundancy, while denormalized databases are designed to optimize read time. We can denormalize the databases by storing redundant data and avoid doing many joins.
As an example, we have this database. * indicates a primary key.
```sql
Courses: CourseID*, CourseName, TeacherID
Teachers: TeacherID*, TeacherName
Students: StudentID*, StudentName
StudentCourses: CourseID*, StudentID*
```
### Query 1: student enrollment
> Get a list of all students and how many courses each student is enrolled in
```sql
SELECT StudentName, Students.StudentID, count(StudentCourses.CourseID) as [Cnt]
FROM Students LEFT JOIN StudentCourses
ON Students.StudentID = StudentCourses.StudentID
GROUP BY Students.StudentID, Students.StudentName
```
For reasons and incorrect implementations and their justification, see chaper 14 in book.
### Query 2: Teacher class size
> Get a list of all teachers and how many students they teach. If a teacher teaches the same student in two courses, double count the student. Sort the list in descending order of the number of students a teacher teaches
```sql
SELECT TeacherName, isnull(StudentSize.Number, 0)
FROM Teachers LEFT JOIN
(SELECT TeacherID, count(StudentCourses.CourseID) AS [Number]
FROM Courses INNER JOIN StudentCourses
ON Courses.CourseID = StudentCourses.CourseID
GROUP BY Courses.TeacherID) StudentSize
ON Teachers.TeacherID = StudentSize.TeacherID
ORDER BY StudentSize.Number DESC
```
## Small database design
How to design a small database
1. Handle ambiguity: understand exactly what you need to design, consult with the interviewer
2. Define the core objects: typically each core object translates into a table
3. Analyze relationships: how tables are connected to each other
4. Investigate actions: walk through the common actions that will be taken and understand how to store and retrieve the relevant data.
## Large database design
When designing a large, scalable database, joins are generally very slow. You must *denormalize* your data. Duplicate the relevant data in many tables.

114
15. Threads and locks/README.md Normal file
View File

@ -0,0 +1,114 @@
# 15. Threads and locks
## Threads in Java
Every thread in Java is created and controlled by a unique object of the Java.lang.Thread class. When a standalone application is run, a user thread is automatically created to execute the `main()` method. This thread is called the main thread.
In Java, we can implement threads in two ways:
1. By implementing the java.lang.Runnable interface
2. By extending the java.lang.Thread class
### Implementing the runnable interface
```java
public interface Rnunable {
void run();
}
```
1. Create a class which implements the Runnable interface. An object of this class is a Runnable object.
2. Create an object of type Thread by passing a Runnable object as argument to the Thread constructor. The Thread object now has a Runnable object that implements the run() method.
3. The start() method is invoked on the Thread object created in the previosu step.
```java
public class RunnableThreadExample implements Runnable {
public int count = 0;
public void run() {
System.out.println("RunnableThread starting");
try {
while (count < 5) {
Thread.sleep(500);
count++;
}
} catch (InterruptedException exc) {
System.out.println("RunnableThread interrupted");
}
System.out.println("RunnableThread terminating");
}
}
public static void main(String[] args) {
RunnableThreadExample instance = new RunnableThreadExample();
Thread thread = new Thread(instance);
thread.start();
/* wait until above thread counts to 5 */
while (instance.count != 5) {
try {
Thread.sleep(250);
} catch {InterruptedException exc} {
exc.printStackTrace();
}
}
}
```
### Extending the thread class
Or, we can override the run() method of the Thread class.
```java
public class ThreadExample extends Thread {
int count = 0;
public void run() {
System.out.println("Thread starting");
try {
while (count < 5) {
Thread.sleep(500);
System.out.println("In Thread, count is " + count);
count++;
}
} catch (InterruptedException exc) {
System.out.println("Thread interrupted");
}
System.out.println("Thread terminating");
}
}
public class ExampleB {
public static void main(String args[]) {
ThreadExample instance = new ThreadExample();
instance.start();
while (instance.count != 5) {
try {
Thread.sleep(250);
} catch (InterruptedException exc) {
exc.printStackTrace();
}
}
}
}
```
## Synchronization and locks
Threads within a given process share ths ame memory space. It enables threads to share data, but it can create issues when the two threads modify a resource at the same time.
With the `synchronized` keyword, it can be applied to methods and code blocks, and it restricts multiple threads from executing the code simultaneously on the *same object*.
For more granular control, we can use a lock, which is used to synchronize access to a shared resource by associating the resource with the lock. A thread gets access to a shared resource by first acquiring the lock associated with the resource. At any given time, at most one thread can hold the lock and therefore, only one thread can access the shared resource.
## Deadlocks and deadlock prevention
In a deadlock situation, a thread is waiting for an object lock that another thread holds, and this second thread is waiting the an object lock that the first thread holds. In order for a deadlock to occur, all the following conditions must meet:
1. Mutual exclusion: only one process can access a resource at a given time
2. Hold and wait: processes already holding a resource can request additional resources, without relinquishing their current resources
3. No preemption: One process cannot forcibly remove another process' resource
4. Circular wait: 2+ processes from a circular chain where each process is waiting on another resource in the chain.
Deadlock prevention entails removing any of the above conditions.