#lang racket

(define/contract (smallest-range-i nums k)
  (-> (listof exact-integer?) exact-integer? exact-integer?)
  (if (<= (length nums) 1) 0
    (let ([mi (apply min nums)]
          [ma (apply max nums)])
      (for*/fold
        ([c ma])
        ([i (in-range (+ k 1))]
         [j (in-range (+ k 1))])
        (min c (abs (- (- ma i) (+ mi j))))
        )
      )
    )
  )

(define (main)
  (define (r l k e)
    (display
      (format
        "(smallest-range-i ~a ~a) = ~a | Exp: ~a\n"
        l k (smallest-range-i l k) e
        )
      )
    )
  (r '(1) 0 0)
  (r '(0 10) 2 6)
  (r '(1 3 6) 3 0)
  (r '(506 4763 8681 4243 4040 8587 9235 442 1865 2820) 5899 0)
  )

(main)