Racket solution for http://java.dzone.com/articles/my-favorite-coding-interview

gistfile1.rkt

#lang racket

(define (run-length n)
  (let ([run-char #f]
        [run-len 0])
    (λ(c) 
      (if (equal? c run-char)
          (set! run-len (+ run-len 1))                 
          (begin (set! run-len 1)
                 (set! run-char c)))
      (<= run-len n))))

(define (remove-extra-consecutive s i)
  (list->string
   (filter (run-length i)
           (string->list s))))

(remove-extra-consecutive "aaab" 2)
(remove-extra-consecutive "aabb" 1)
(remove-extra-consecutive "aabbaa" 1)