Leetcode longest palindrome racket

Challenge

Solution

(require srfi/1)

(define (expand-from-center s l r)

  (let ([terminals-equal?

         (equal? (string-ref s l)

            (string-ref s r))]) 

    ;;(printf " ~v ~v ~v ~v ~v " l r (+ (- r l) 1) (string-ref s l) (string-ref s r))

    (cond [(and terminals-equal? (or (= l 0) (= r (- (string-length s) 1)))) (+ (- r l) 1)]

     [terminals-equal? (expand-from-center s (- l 1) (+ 1 r))]

     [else (- (- r l) 1)]

      )))

(define 

 (longest-palindrome s)

  (if (> (string-length s) 1) 

      (let* ([sizes (map (lambda (i) (max (expand-from-center s i i)

                        (expand-from-center s i (+ i 1))))

       (range (- (string-length s) 1)))]

               [max-size (apply max sizes)]

               [max-size-index (list-index (curry equal? max-size) sizes)]

               )

    (printf " ~v ~v ~v ~v " max-size max-size-index (+ (- 1 (remainder max-size 2)) 

                                                       (- max-size-index (quotient max-size 2)))

            (+ max-size-index (quotient max-size 2) 1)

            )

    (substring s (+ (- 1 (remainder max-size 2)) (- max-size-index (quotient max-size 2)))

                              (+ max-size-index (quotient max-size 2) 1)))

      s))