P15 (**) Replicate the elements of a list a given number of times.
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问题描述
sash> (repli '(a b c) 3)sash> (a a a b b b c c c)解法
(define repli (lambda (ls n) (let f ([s ls] [m n]) (if (null? s) '() (if (zero? m) (f (cdr s) n) (let ([e (car s)]) (cons e (f s (- m 1)))))))))与上一个P14类似，也可将每个元素重复形成相应的子列表，然后用append拼接起来。
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