Project Euler

[ホーム](https://redmine.noppi.jp) - [[Wiki|Project Euler]]

# [[Problem 10]]

```scheme

#!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 (eratosthenes-sub! table erase-num)

  (assert (vector-ref table erase-num))

  (let loop ((current (* erase-num 2)))

    (cond

      [(<= (vector-length table) current) table]

      [else

        (vector-set! table current #f)

        (loop (+ current erase-num))])))

(define (eratosthenes num)

  (let ((table (make-vector num #t))

        (count (isqrt (sub1 num))))

    (vector-set! table 0 #f)

    (vector-set! table 1 #f)

    (let loop ((index 2) (table table))

      (cond

        [(< count index) table]

        [(vector-ref table index)

         (loop (add1 index) (eratosthenes-sub! table index))]

        [else (loop (add1 index) table)]))))

(define answer-10

  (sum-prime (eratosthenes 2000001)))

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

```