[英]Adding The Sum Of Nested List In Scheme
I'm using scheme. 我正在使用计划。 I'm having no problems in finding the sum of a certain list but I'm quite having trouble in adding the sum when a list has a list in it or AKA Nested List. 我找到某个列表的总和没有问题,但是当列表中有列表或AKA嵌套列表时,我很难添加总和。
(define (my-summation li)
(if (null? li)
0
((if (list? (car li)) (my-summation (car li))
(+ (car li) (my-summation (cdr li)))))))
This was my input and this was the result of the error. 这是我的输入,这是错误的结果。 Scheme is my weakness since it involves recursion but I can't seem to find the problem. Scheme是我的弱点,因为它涉及递归,但我似乎无法找到问题。
> (my-summation '(6 3 -2 5 '(4 2 -3) 4 ))
function call: expected a function after the open parenthesis, but received -3
Its in the parentheses, you have an extra set around the if
. 它在括号中,你有一个额外的设置围绕if
。 Also you don't need to quote a list when it is in a quoted list. 此外,当它在引用列表中时,您不需要引用列表。 And the (list? (car li))
case was incorrect, it should sum the element and the rest of the list. 并且(list? (car li))
案例不正确,它应该对元素和列表的其余部分求和。
(define (my-summation li)
(if (null? li)
0
(if (list? (car li))
(+ (my-summation (car li)) (my-summation (cdr li)))
(+ (car li) (my-summation (cdr li))))))
(my-summation '(6 3 -2 5 (4 2 -3) 4))
Results in a sum of 19
. 结果总和为19
。
An alternative solution: 替代解决方案:
(define (sum-list xs)
(define (loop sum-so-far xs)
(cond
[(null? xs) sum-so-far] ; no-more-elements
[(pair? (car xs)) (loop (+ sum-so-far (sum-list (car xs))) ; the first element is a sublist
(cdr xs))] ; so sum-list computes its sum
[else (loop (+ sum-so-far (car xs)) ; the first element is a number
(cdr xs))])) ; so it is added directly
(loop 0 xs))
(sum-list '(6 3 -2 5 (4 2 -3) 4)) ; note: no quote in the middle
; ==> 19
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.