; treaps
(define (take n xs)
(let loop ((n n) (xs xs) (ys '()))
(if (or (zero? n) (null? xs))
(reverse ys)
(loop (- n 1) (cdr xs)
(cons (car xs) ys)))))
(define rand
(let* ((a 3141592653) (c 2718281829)
(m (expt 2 35)) (x 5772156649)
(next (lambda ()
(let ((x-prime (modulo (+ (* a x) c) m)))
(set! x x-prime) x-prime)))
(k 103)
(v (list->vector (reverse
(let loop ((i k) (vs (list x)))
(if (= i 1) vs
(loop (- i 1) (cons (next) vs)))))))
(y (next))
(init (lambda (s)
(set! x s) (vector-set! v 0 x)
(do ((i 1 (+ i 1))) ((= i k))
(vector-set! v i (next))))))
(lambda seed
(cond ((null? seed)
(let* ((j (quotient (* k y) m))
(q (vector-ref v j)))
(set! y q)
(vector-set! v j (next)) (/ y m)))
((eq? (car seed) 'get) (list a c m x y k v))
((eq? (car seed) 'set)
(let ((state (cadr seed)))
(set! a (list-ref state 0))
(set! c (list-ref state 1))
(set! m (list-ref state 2))
(set! x (list-ref state 3))
(set! y (list-ref state 4))
(set! k (list-ref state 5))
(set! v (list-ref state 6))))
(else (init (modulo (numerator
(inexact->exact (car seed))) m))
(rand))))))
(define (treap k p v l r) (vector k p v l r))
(define (key t) (vector-ref t 0))
(define (prio t) (vector-ref t 1))
(define (val t) (vector-ref t 2))
(define (lkid t) (vector-ref t 3))
(define (rkid t) (vector-ref t 4))
(define nil (vector 'nil -1 'nil 'nil 'nil))
(define (nil! k) (vector-set! nil 0 k))
(define (nil? t) (eq? t nil))
(define (leaf? t) (and (nil? (lkid t)) (nil? (rkid t))))
(define (leaf-or-nil? t) (eq? (lkid t) (rkid t)))
(define (rot-left t)
(let ((l (treap (key t) (prio t) (val t) (lkid t) (lkid (rkid t)))))
(treap (key (rkid t)) (prio (rkid t)) (val (rkid t)) l (rkid (rkid t)))))
(define (rot-right t)
(let ((r (treap (key t) (prio t) (val t) (rkid (lkid t)) (rkid t))))
(treap (key (lkid t)) (prio (lkid t)) (val (lkid t)) (lkid (lkid t)) r)))
(define (lookup lt? t k)
(cond ((nil? t) #f)
((lt? k (key t)) (lookup lt? (lkid t) k))
((lt? (key t) k) (lookup lt? (rkid t) k))
(else (cons k (val t)))))
(define (insert lt? t k v)
(cond ((nil? t) (treap k (rand) v nil nil))
((lt? k (key t))
(let ((t (treap (key t) (prio t) (val t) (insert lt? (lkid t) k v) (rkid t))))
(if (< (prio t) (prio (lkid t))) (rot-right t) t)))
((lt? (key t) k)
(let ((t (treap (key t) (prio t) (val t) (lkid t) (insert lt? (rkid t) k v))))
(if (< (prio t) (prio (rkid t))) (rot-left t) t)))
(else (treap k (prio t) v (lkid t) (rkid t)))))
(define (deroot t)
(cond ((leaf-or-nil? t) nil)
((< (prio (lkid t)) (prio (rkid t)))
(let ((t (rot-left t)))
(treap (key t) (prio t) (val t) (deroot (lkid t)) (rkid t))))
(else (let ((t (rot-right t)))
(treap (key t) (prio t) (val t) (lkid t) (deroot (rkid t)))))))
(define (delete lt? t k)
(nil! k)
(let delete ((t t))
(cond ((lt? k (key t))
(treap (key t) (prio t) (val t) (delete (lkid t)) (rkid t)))
((lt? (key t) k)
(treap (key t) (prio t) (val t) (lkid t) (delete (rkid t))))
(else (deroot t)))))
(define (update lt? t f k v)
(cond ((nil? t) (treap k (rand) v nil nil))
((lt? k (key t))
(let ((t (treap (key t) (prio t) (val t) (update lt? (lkid t) f k v) (rkid t))))
(if (< (prio t) (prio (lkid t))) (rot-right t) t)))
((lt? (key t) k)
(let ((t (treap (key t) (prio t) (val t) (lkid t) (update lt? (rkid t) f k v))))
(if (< (prio t) (prio (rkid t))) (rot-left t) t)))
(else (treap k (prio t) (f k (val t)) (lkid t) (rkid t)))))
(define (enlist t)
(if (nil? t) '()
(append (enlist (lkid t)) (list (cons (key t) (val t))) (enlist (rkid t)))))
(define (read-word)
(let loop ((c (read-char)) (cs '()))
(cond ((eof-object? c)
(if (null? cs) c
(list->string (reverse cs))))
((char-alphabetic? c)
(loop (read-char) (cons (char-downcase c) cs)))
((pair? cs) (list->string (reverse cs)))
(else (loop (read-char) cs)))))
(define (word-freq n file-name)
(define (freq-gt? a b) (> (cdr a) (cdr b)))
(with-input-from-file file-name
(lambda ()
(let loop ((word (read-word)) (freqs nil))
(if (eof-object? word)
(take n (sort freq-gt? (enlist freqs)))
(loop (read-word) (update string<? freqs (lambda (k v) (+ v 1)) word 1)))))))