String Transformer

Level: Advanced 60–90 min

Concepts: AlgorithmsDesign PatternsEdge CasesRefactoring

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Build a string transformer that supports chainable operations. Each operation transforms the input string and passes the result to the next operation.

Requirements

1. Create a StringTransformer that takes an initial string
2. Support the following operations, all chainable:
   • capitalise() — capitalise the first letter of each word
   • reverse() — reverse the entire string
   • removeWhitespace() — remove all whitespace
   • snakeCase() — convert to snake_case
   • camelCase() — convert to camelCase
   • truncate(n) — truncate to n characters, adding ”…” if truncated
   • repeat(n) — repeat the string n times with a space separator
   • replace(target, replacement) — replace all occurrences
3. result() returns the final transformed string
4. Operations are applied in order

Test Cases

Input	Operations	Result
”hello world”	capitalise()	“Hello World"
"hello world”	reverse()	“dlrow olleh"
"hello world”	removeWhitespace()	“helloworld"
"hello world”	snakeCase()	“hello_world"
"Hello World”	camelCase()	“helloWorld"
"hello world”	truncate(5)	“hello…"
"hello world”	truncate(50)	“hello world"
"ha”	repeat(3)	“ha ha ha"
"hello world”	capitalise().reverse()	“dlroW olleH"
"hello world”	snakeCase().capitalise()	“Hello_World"
""	capitalise()	""
"HELLO WORLD”	camelCase()	“helloWorld"
"hello-world test”	snakeCase()	“hello_world_test”

Bonus

• Add cipher(n) — apply a Caesar cipher shifting each letter by n positions
• Add slug() — convert to URL-friendly slug (lowercase, hyphens, no special characters)
• Add mask(n) — mask all but the last n characters with asterisks (useful for credit cards, emails)
• Make the transformer immutable — each operation returns a new transformer, allowing branching transformations