String Basics and Memory Representation in DSA Typescript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of String Concatenation and Length

What is the output of the following TypeScript code?

DSA Typescript

const s1 = "hello";
const s2 = "world";
const s3 = s1 + " " + s2;
console.log(s3.length);

A 11

B 10

C 5

D 0

💡 Hint

Count all characters including the space between words.

The string s3 is "hello world" which has 11 characters including the space.

❓ Predict Output

intermediate

String Immutability Effect

What will be printed after running this TypeScript code?

DSA Typescript

let str = "abc";
str[0] = "z";
console.log(str);

A Zbc

B zbc

C Error

D abc

💡 Hint

Strings cannot be changed by index assignment in TypeScript.

Strings are immutable in TypeScript. Assigning to str[0] does nothing, so str remains "abc".

❓ Predict Output

advanced

Memory Representation of String Characters

What is the output of this TypeScript code that prints character codes?

DSA Typescript

const s = "Hi!";
const codes = [];
for (let i = 0; i < s.length; i++) {
  codes.push(s.charCodeAt(i));
}
console.log(codes);

A [72, 105, 33]

B [104, 105, 33]

C [72, 105, 35]

D [104, 105, 35]

💡 Hint

Use ASCII codes: 'H' = 72, 'i' = 105, '!' = 33.

charCodeAt returns the UTF-16 code unit for each character. 'H' is 72, 'i' is 105, '!' is 33.

🧠 Conceptual

advanced

Understanding String Interning

Which statement about string interning in TypeScript/JavaScript is true?

A String interning automatically merges strings with different content.

B Strings are immutable but do not guarantee shared memory references for identical content.

C Strings can be changed after creation if interned.

D Strings with the same content always share the same memory reference.

💡 Hint

Think about immutability and memory sharing behavior in JavaScript strings.

Strings are immutable, but JavaScript engines may or may not share memory for identical strings. This is an implementation detail and not guaranteed.

🔧 Debug

expert

Why does this string slicing code produce unexpected output?

Consider this TypeScript code snippet. What is the output and why?

DSA Typescript

const s = "abcdef";
const slice1 = s.slice(2, 4);
const slice2 = s.slice(4, 2);
console.log(slice1);
console.log(slice2);

A "cd" and "ef" because slice swaps start and end if start > end

B "cd" and "" because slice treats end as 0 if less than start

C "cd" and "" because slice with start > end returns empty string

D "cd" and "" because slice ignores invalid indices

💡 Hint

Check how slice behaves when the start index is greater than the end index.

slice(start, end) returns substring from start up to but not including end. If start > end, it returns empty string.

Practice

1. What does the term immutable mean when talking about strings in TypeScript?

easy

A. Once created, the string cannot be changed.

B. The string can be changed anytime.

C. The string is stored in a mutable array.

D. The string is stored as a number.

Solution

1. Step 1: Understand string immutability

   Strings in TypeScript cannot be changed after creation. Any modification creates a new string.

2. Step 2: Compare options with definition

   Only Once created, the string cannot be changed. correctly states that strings cannot be changed once created.

3. Final Answer:

   Once created, the string cannot be changed. -> Option A

4. Quick Check:

   Immutable means unchangeable = A [OK]

Hint: Remember: strings can't be changed after creation [OK]

Common Mistakes:

• Thinking strings can be changed like arrays
• Confusing mutable and immutable
• Assuming strings are stored as numbers

2. Which of the following is the correct way to declare a string variable in TypeScript?

easy

A. let name: number = 'Alice';

B. let name = 123;

C. let name: string = 'Alice';

D. let name: string = 123;

Solution

1. Step 1: Check variable declaration syntax

   TypeScript uses let variableName: type = value; syntax.

2. Step 2: Match type and value

   let name: string = 'Alice'; declares a string variable with a string value correctly.

3. Final Answer:

   let name: string = 'Alice'; -> Option C

4. Quick Check:

   Correct string declaration = A [OK]

Hint: Match variable type with value type exactly [OK]

Common Mistakes:

• Assigning number to string type
• Missing type annotation
• Using wrong syntax for declaration

3. What will be the output of the following TypeScript code?

let greeting = 'Hello';
greeting[0] = 'Y';
console.log(greeting);

medium

A. Yello

B. undefined

C. Error: Cannot assign to string index

D. Hello

Solution

1. Step 1: Understand string immutability in TypeScript

   Strings cannot be changed by index assignment; such operations do not modify the string.

2. Step 2: Analyze the code behavior

   Assigning greeting[0] = 'Y' does nothing; greeting remains 'Hello'.

3. Final Answer:

   Hello -> Option D

4. Quick Check:

   Strings immutable, no change = Hello [OK]

Hint: Strings can't be changed by index assignment [OK]

Common Mistakes:

• Expecting first letter to change
• Thinking string is mutable like array
• Assuming error will be thrown

4. What best describes the result of the following TypeScript code snippet:

let str: string = 'Test';
str[1] = 'a';
console.log(str);

medium

A. No error, output is 'Test'

B. TypeError: Cannot assign to string index

C. SyntaxError: Invalid assignment

D. ReferenceError: str is not defined

Solution

1. Step 1: Check string mutability rules

   Strings are immutable; assigning to an index does nothing.

2. Step 2: Analyze the code behavior

   str[1] = 'a' does nothing; str remains 'Test', console.log outputs 'Test'. No error.

3. Final Answer:

   No error, output is 'Test' -> Option A

4. Quick Check:

   Strings immutable, index assignment ignored = 'Test' [OK]

Hint: Strings cannot be changed by index assignment [OK]

Common Mistakes:

• Assuming no error and string changes
• Confusing syntax error with runtime error
• Expecting ReferenceError

5. Given the following code, what will be the output?

let s1 = 'abc';
let s2 = s1 + 'd';
console.log(s1);
console.log(s2);

Choose the correct output considering string immutability and memory representation.

hard

A. abcabc

B. abcabcd

C. abcdabcd

D. Error at runtime

Solution

1. Step 1: Understand string concatenation and immutability

   Concatenating strings creates a new string; original strings remain unchanged.

2. Step 2: Trace variable values after operations

   s1 remains 'abc'; s2 becomes 'abcd'.

3. Final Answer:

   abc
   abcd -> Option B

4. Quick Check:

   Original unchanged, new string created = abc and abcd [OK]

Hint: Concatenation creates new string; originals stay same [OK]

Common Mistakes:

• Expecting s1 to change after concatenation
• Thinking concatenation modifies original string
• Assuming runtime error on concatenation