blob: 5797b0c64d1173829b24dcc67e8526ffed6f8abf (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
|
;;;
;;; Problem 16: Power digit sum
;;;
;;; https://projecteuler.net/problem=16
(define (digit-sum n)
(let loop ((m 1)
(sum 0))
(if (> (expt 10 (1- m)) n)
sum
(loop (1+ m) (+ sum (digit m n))))))
(define (digit m n)
"Return the Mth digit of N."
;; Tenths place, hundreds place, etc.
(let ((place (expt 10 (1- m))))
(/ (- (modulo n (expt 10 m))
(modulo n place))
place)))
(digit-sum (expt 2 1000))
|
