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Day 10: Use atan2 instead of dividing into different cases.

This commit is contained in:
Jonathan Chan 2019-12-10 14:36:13 -08:00
parent 80b25a4095
commit 56aacd00fd
1 changed files with 6 additions and 12 deletions
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18
src/10.rkt
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@ -51,18 +51,12 @@
(list-ref in-views index))))
(define (offset<? xy1 xy2)
(let ([x1 (first xy1)]
[y1 (second xy1)]
[x2 (first xy2)]
[y2 (second xy2)])
(or ; (0, -) < (+, y) < (0, +) < (-, y)
(and (zero? x1) (negative? y1))
(and (positive? x1)
(or (negative? x2)
(and (zero? x2) (positive? y2))))
(and (zero? x1) (negative? x2))
(and (nzero? x1) (nzero? x2)
(< (atan (/ y1 x1)) (atan (/ y2 x2)))))))
(let* ([x1 (first xy1)] [y1 (second xy1)]
[x2 (first xy2)] [y2 (second xy2)]
[θ1 (atan y1 x1)] [θ2 (atan y2 x2)]
[θ1 (+ θ1 (if (< θ1 (/ pi -2)) (* 2 pi) 0))]
[θ2 (+ θ2 (if (< θ2 (/ pi -2)) (* 2 pi) 0))])
(< θ1 θ2)))
(define part2
(let* ([offsets (map (λ (ast) (zip - ast location)) in-view)]