https://bgm.tv/group/topic/350078

remove-palindrome.rkt

#lang racket
(define (remove-palindrome s)
  (define f
    (cachedproc
     (lambda (i j)
       (cond
         [(equal? i j) 0]
         [(equal? (+ i 1) j) 1]
         [(and (equal? (+ i 2) j) (equal? (list-ref s i) (list-ref s (- j 1)))) 1]
         [(equal? (list-ref s i) (list-ref s (- j 1))) (f (+ i 1) (- j 1))]
         [else (apply min (map (lambda (k) (+ (f i k) (f k j))) (range (+ i 1) j)))]))))
  (f 0 (length s)))

(define (cachedproc func)
  (let ([h (make-hash)])
    (define (wrapped . w)
      (hash-ref! h w (lambda () (apply func w))))
    wrapped))