[Scheme] Verify palindromic

[Scheme] Verify palindromic

topic

Write a recursive function to determine if the elements of a list form a palindrome(回文: 从左读与从右读都一样). For example:
palindrome : List -> Bool
> (palindrome ‘(1 1 2 2 3 3))
#f
> (palindrome ‘(1 2 2 2 1))
#t
> (palindrome ‘(1 a b a 1))
#t
Note : For simplicity, you may assume that the list to check contains only atoms. I.e., no nested list and you can use “eq?” to test for equality

The problem simply,
the argument is a list, our function will return this list whether they have the characteristics of palindromes.

The idea
idea most people should start with me, like, what to write this recursive? Not reverse his party to get thing?

	(define (palindrome-reverse a-list)
  (equal? a-list (reverse a-list)))

ya ... Yes, indeed this line to meet our needs.

But mention the topic, please write a recursive function to do,
the class also repeatedly mentioned, high-order function of these built-in function, but also by one a smaller scheme function composition.

So, write your own hands it ~ reverse function

design ideas recursive function

1. Judgment palindrome, which is equal to its own list upside down, return true, does not mean the return false.
2. recursive design ideas, how upside down:
   Like to meet tail-recursion, we will start with a accumulating parameter, to put every scratch results.
   Each taking (car list), then append to pay attention to the order, the result is to be added to the front of, or behind.
   Since we want to do backwards, that is to (append (the car list of element) result)
3. When cdr list is empty, it means that all take over, return our results

So I wrote code a long way:

	;case 1: (palindrome '(1 1 2 2 3 3)) => #f
;case 2: (palindrome '(1 2 2 2 1)) => #t
;case 3: (palindrome '(1 a b a 1)) => #t
(define (tailReverse a-list result)
  (if (null? a-list) 
      result
      (tailReverse (cdr a-list) (append (list (car a-list)) result)))
)

(define (palindrome a-list)
  (equal? a-list (tailReverse a-list '()))    
)

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Original: Large column  [Scheme] verification palindrome