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(define-module (nsd)
#:export (nsd
nsd-generator
calculate-seq-length))
(define (nsd n)
"Given dimension N of a square, calculates and sums
an appropriately sized sequence."
(apply + (nsd-generator (calculate-seq-length n))))
(define (nsd-generator k)
"Generates a sequence of numbers corresponding to the
diagonals in a square. See README for more details on how
this is used to solve the problem."
(let loop ((i 0)
(lst '(1)))
(if (>= (1+ i) k)
(reverse lst)
(loop (1+ i)
(cons (+ (car lst) (* 2 (1+ (quotient i 4)))) lst)))))
(define (calculate-seq-length n)
"Calculates the size of the sequence. This is equal to
the length of the two diagonals, minus one for the overlapping
center."
(1- (* 2 n)))
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