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joachimschmidt557 2020-01-29 16:30:13 +01:00
parent fbdc710918
commit 7bbf3a5070
5 changed files with 57 additions and 1 deletions
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substr.rkt Normal file
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;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-advanced-reader.ss" "lang")((modname substr) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #t #t none #f () #f)))
(define (is-substring? s sub)
(is-substring-expl? (explode s) (explode sub) (explode sub)))
(define (is-substring-expl? s sub backup)
(cond [(empty? sub) #t]
[(empty? s) #f]
[(equal? (first s) (first sub))
(is-substring-expl? (rest s) (rest sub) backup)]
[(equal? (first s) (first backup))
(is-substring-expl? (rest s) (rest backup) backup)]
[else (is-substring-expl? (rest s) sub backup)]))