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;;03:39
;;04:07 Solved
;;05:24 Painful refactorins
(ql:quickload '(fiveam arrows transducers))
(defparameter eg-input "0 3 6 9 12 15
1 3 6 10 15 21
10 13 16 21 30 45")
(defun row-reducer (row)
(mapcar #'- (cdr row) row))
(defun terminal-p (row)
(every #'= (cdr row) row))
(defun get-coefs (row &optional (acc 0))
(if (terminal-p row)
(+ (car (last row)) acc)
(get-coefs (row-reducer row) (+ (car (last row)) acc))))
(defun parse-line (line)
(mapcar #'parse-integer (uiop:split-string line)))
(defun solver (lines order)
(reduce #'+
lines
:key (alexandria:compose #'get-coefs order #'parse-line)))
(fiveam:test solutions
(fiveam:is (= 114 (solver (uiop:split-string eg-input :separator '(#\Newline))
#'identity)))
(fiveam:is (= 2105961943 (solver (uiop:read-file-lines "input")
#'identity)))
(fiveam:is (= 2 (solver (uiop:split-string eg-input :separator '(#\Newline))
#'nreverse)))
(fiveam:is (= 1019 (solver (uiop:read-file-lines "input")
#'nreverse))))
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