Check for duplicates

Detect duplicate characters in strings and duplicate items in lists using Clarity

;; Check for duplicate characters in a string
(define-read-only (has-duplicate-chars? (input (string-ascii 200)))
  (is-none (fold dup input (slice? (concat input "|END") u1 (+ (len input) u4))))
)

(define-private (dup (ch (string-ascii 1)) (out (optional (string-ascii 204))))
  (match out out_some 
    (match (index-of? (unwrap-panic (slice? out_some u0 (- (len out_some) u4))) ch) 
      found none 
      (slice? out_some u1 (len out_some))
    )
    out
  )
)

;; Example usage
(has-duplicate-chars? "hello") ;; Returns true (duplicate 'l')
(has-duplicate-chars? "world") ;; Returns false (no duplicates)

Use cases

Validating usernames for uniqueness of characters
Checking NFT trait uniqueness in collections
Preventing duplicate entries in voting systems
Ensuring unique identifiers in lists

Key concepts

The duplicate detection uses different strategies:

Strings: Uses fold with index-of? to find repeated characters
Lists: Checks if elements appear again in the remaining list
Optimization: Early exit on first duplicate found