Determine if a string has all unique characters: Difference between revisions

=={{header|Racket}}==

<lang racket>#lang racket

(define (first-non-unique-element.index seq)

(let/ec ret

(for/fold ((es (hash))) ((e seq) (i (in-naturals)))

(if (hash-has-key? es e) (ret (list e (hash-ref es e) i)) (hash-set es e i)))

#f))

(define (report-if-a-string-has-all-unique-characters str)

(printf "~s (length ~a): ~a~%" str (string-length str)

(match (first-non-unique-element.index str)

[#f "contains all unique characters"]

[(list e i i′) (format "has character '~a' (0x~a) at index ~a (first seen at ~a)"

e (number->string (char->integer e) 16) i′ i)])))

(module+ main

(for-each report-if-a-string-has-all-unique-characters

(list "" "." "abcABC" "XYZ ZYX"

"1234567890ABCDEFGHIJKLMN0PQRSTUVWXYZ")))

</lang>

{{out}}

<pre>"" (length 0): contains all unique characters

"." (length 1): contains all unique characters

"abcABC" (length 6): contains all unique characters

"XYZ ZYX" (length 7): has character 'Z' (0x5a) at index 4 (first seen at 2)

"1234567890ABCDEFGHIJKLMN0PQRSTUVWXYZ" (length 36): has character '0' (0x30) at index 24 (first seen at 9)</pre>