CTE questions

`String.prototype.charAt` returns the character at a specified index in a string. If the index is out of range, it returns an empty string. 

const str = 'hello';
const char = str.charAt(1);
console.log(char); // 'e'

The `@Injectable` decorator in Angular is used to mark a class as a service that can participate in Angular's dependency injection system. When applied to a class, it indicates that the class can be injected into other classes via the constructor, allowing it to be used as a service. This decorator ensures that Angular can create and manage instances of the class and handle its dependencies, enabling efficient and modular code. `@Injectable` is essential for services, as it facilitates their registration and injection into components, other services, or modules.

SQL Injection occurs when an attacker inserts malicious SQL code into a query, which can compromise the database. Prevent SQL Injection by using parameterized queries or prepared statements, validating and escaping user input, and implementing robust input validation and sanitization practices.

An Invalid Path Variable error occurs when a path variable in a URL does not match the expected format or value. Verify that path variables are correctly formatted and correspond to the expected values in routing configurations. Implement validation to ensure that variables meet expected criteria.

An Invalid Content-Type error occurs when the Content-Type header in a request does not match the expected type, such as sending JSON data with an incorrect Content-Type. Ensure that the Content-Type header is correctly set to match the request payload and validate it on the server side to handle data appropriately.

Use a hash map to count the frequency of each character, then iterate through the string to find the first character with a count of 1. For example, in 'swiss', the first non-repeating character is 'w'.

Use Depth-First Search with a tracking mechanism for visited nodes. If a node is revisited during the same DFS traversal, a cycle exists. For example, in a graph with edges 1 -> 2 -> 3 -> 1, a cycle is detected.

Use topological sorting to order nodes and then apply dynamic programming to find the longest path. For example, in a DAG with edges 1 -> 2, 1 -> 3, 2 -> 4, 3 -> 4, the longest path is 1 -> 2 -> 4 or 1 -> 3 -> 4.

XML has several key features: 1. Simplicity: It is easy to understand and read. 2. Extensibility: You can define your own tags. 3. Structure: Data is stored in a hierarchical format. 4. Platform independent: It can be used across different systems. 5. Human and machine-readable: XML is easily readable by both humans and machines. 6. Self-descriptive: Tags describe the data they enclose. 

 <person>
  <name>John</name>
  <age>30</age>
</person>