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  • Count-Trailing-Zeros(1200) ==> 2 _________ in Scheme, Gauche, Common Li

    From Hen Hanna@21:1/5 to All on Wed Sep 7 11:15:28 2022
    Count-Trailing-Zeros(x) ----- Can I use Log(x) to see if X is equal to ( Integer * 10 ^ k) ???

    How do you do this in Scheme, Gauche, Common Lisp ?


    --------- is there a simple string function that counts the leftmost 0's ???



    __________________
    Count how many zeros are at the end of an int:

    def end_zeros(num):
    s = str(num)
    return len(s) - len(s.rstrip("0"))


    print(end_zeros(10)) # ==> 1
    print(end_zeros(101)) # ==> 0
    print(end_zeros(245)) # ==> 0
    print(end_zeros(100100)) # ==> 2

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Hen Hanna@21:1/5 to Hen Hanna on Wed Sep 7 15:28:16 2022
    On Wednesday, September 7, 2022 at 11:15:30 AM UTC-7, Hen Hanna wrote:
    Count-Trailing-Zeros(x) ----- Can I use Log(x) to see if X is equal to ( Integer * 10 ^ k) ???

    How do you do this in Scheme, Gauche, Common Lisp ?


    --------- is there a simple string function that counts the leftmost 0's ???



    __________________
    Count how many zeros are at the end of an int:

    def end_zeros(num):
    s = str(num)
    return len(s) - len(s.rstrip("0"))


    print(end_zeros(10)) # ==> 1
    print(end_zeros(101)) # ==> 0
    print(end_zeros(245)) # ==> 0
    print(end_zeros(100100)) # ==> 2


    two ideas:

    1. i can use string-skip-right to imitate the Python code above.

    2. The following works:

    (define (Count-end-0 x)
    (cdr (fold-right ce0 '(#t . 0) (string->list (number->string x)))))

    (define (ce0 c y)
    (if (car y)
    (if (char=? c #\0)
    (cons #t (+ 1 (cdr y)))
    (cons #f (cdr y)))
    y))

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Paul Rubin@21:1/5 to Hen Hanna on Wed Sep 7 17:19:55 2022
    Hen Hanna <[email protected]> writes:
    --------- is there a simple string function that counts the leftmost
    0's ???

    1. I think you mean rightmost zeros.
    2. Converting to a string and counting the '0' chars is pretty ugly.

    I'd just use simple arithmetic and tail recursion (the Scheme-ish way
    to implement a loop):

    (define (nz n)
    (define (go n a)
    (if (= (remainder n 10) 0)
    (go (quotient n 10) (1+ a))
    a))
    (go n 0))

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Hen Hanna@21:1/5 to Paul Rubin on Fri Sep 9 18:53:27 2022
    On Wednesday, September 7, 2022 at 5:20:00 PM UTC-7, Paul Rubin wrote:
    Hen Hanna <[email protected]> writes:
    --------- is there a simple string function that counts the leftmost
    0's ???
    1. I think you mean rightmost zeros.
    2. Converting to a string and counting the '0' chars is pretty ugly.

    I'd just use simple arithmetic and tail recursion (the Scheme-ish way
    to implement a loop):

    (define (nz n)
    (define (go n a)
    (if (= (remainder n 10) 0)
    (go (quotient n 10) (1+ a))
    a))
    (go n 0))


    Thank you.... i wonder where internal definittions (5.3.2. Internal definitions in R7RS)
    originally came from.....

    Were they in MacLISP ?

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  • From Paul Rubin@21:1/5 to Hen Hanna on Sat Sep 10 16:17:44 2022
    Hen Hanna <[email protected]> writes:
    Thank you.... i wonder where internal definittions (5.3.2. Internal definitions in R7RS) originally came from..... Were they in MacLISP ?

    I think was possible to write an internal lambda in Maclisp using FLET
    but it wouldn't have been idiomatic. Using internal functions like that
    is typical of functional programming though, and Scheme was one of the
    early promoters of that style.

    I never used Maclisp but at least originally, it ran on machines that we
    would now consider quite memory constrained. So it might have been more conventional (though uglier) to use a mutable cell. This is Emacs Lisp
    which sort of resembles Maclisp:

    (defun nz (n)
    (let ((a 0))
    (while (= (mod n 10) 0)
    (setq a (1+ a)
    n (/ n 10)))
    a))

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)