Programming Praxis 19 Aug 2011 (first non-repeating char) solution in PLT Racket
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#lang racket | |
(define (first-uniq chars) | |
(when (empty? chars) | |
(raise "There are no unique letters")) | |
(let ([c (first chars)]) | |
(if (memq c (rest chars)) ; MEMQ is like MEMBER with EQ? | |
(first-uniq (remq* (list c) chars)) ; N.B the tail-recursion here | |
c))) | |
(require rackunit) | |
(check-equal? (first-uniq (string->list "aabcbcdeef")) | |
#\d) | |
(check-equal? (first-uniq (string->list "faabcbcdeef")) | |
#\d) | |
(check-equal? (first-uniq (string->list "aabcbcdeefd")) | |
#\f) |
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