ホーム - Project Euler

Problem 10¶

#!r6rs
#!chezscheme

(import (chezscheme))

(define (sum-prime prime?-table)
  (let* ((len (vector-length prime?-table))
         (index-list (iota len))
         (prime?-list (vector->list prime?-table)))
    (fold-left
      (lambda (sum index prime?)
        (if prime?
          (+ sum index)
          sum))
      0
      index-list
      prime?-list)))

(define answer-10
  (let ((table (make-vector 2000001 #t))
        (count (isqrt 2000000)))
    (vector-set! table 0 #f)
    (vector-set! table 1 #f)

    (let loop1 ((index 2))
      (cond
        [(< count index) (sum-prime table)]
        [(vector-ref table index)
         (let loop2 ((current (* index 2)))
           (cond
             [(< 2000000 current)
              (loop1 (add1 index))]
             [else
               (vector-set! table current #f)
               (loop2 (+ current index))]))]
        [else (loop1 (add1 index))]))))

(printf "10: ~D~%" answer-10)