Language: C C++ D Haskell Lua OCaml PHP Perl Plain Text Python Ruby Scheme Tcl ; remove singleton (define (remove-singleton c str) (define (none ins outs) (cond ((null? ins) outs) ((char=? (car ins) c) (one (cdr ins) outs)) (else (none (cdr ins) (cons (car ins) outs))))) (define (one ins outs) (cond ((null? ins) outs) ((char=? (car ins) c) (many (cdr ins) (cons c (cons c outs)))) (else (none (cdr ins) (cons (car ins) outs))))) (define (many ins outs) (cond ((null? ins) outs) ((char=? (car ins) c) (many (cdr ins) (cons c outs))) (else (none (cdr ins) (cons (car ins) outs))))) (list->string (reverse (none (string->list str) (list))))) (define-syntax assert (syntax-rules () ((assert expr result) (if (not (equal? expr result)) (for-each display `( #\newline "failed assertion:" #\newline expr #\newline "expected: " ,result #\newline "returned: " ,expr #\newline)))))) (define (test-remove-singleton) ; no news is good news (assert (remove-singleton #\X "") "") (assert (remove-singleton #\X "X") "") (assert (remove-singleton #\X "XX") "XX") (assert (remove-singleton #\X "XXX") "XXX") (assert (remove-singleton #\X "abcd") "abcd") (assert (remove-singleton #\X "Xabcd") "abcd") (assert (remove-singleton #\X "XXabcd") "XXabcd") (assert (remove-singleton #\X "XXXabcd") "XXXabcd") (assert (remove-singleton #\X "abcdX") "abcd") (assert (remove-singleton #\X "abcdXX") "abcdXX") (assert (remove-singleton #\X "abcdXXX") "abcdXXX") (assert (remove-singleton #\X "abXcd") "abcd") (assert (remove-singleton #\X "abXXcd") "abXXcd") (assert (remove-singleton #\X "abXXXcd") "abXXXcd") (assert (remove-singleton #\X "XabXcdX") "abcd") (assert (remove-singleton #\X "XXabXXcdXX") "XXabXXcdXX") (assert (remove-singleton #\X "XXXabXXXcdXXX") "XXXabXXXcdXXX")) (test-remove-singleton) Private [?] Run code Submit