day 15 part 2. using INTERVALS

day15.lisp

@@ -18,6 +18,10 @@
   (and (= (x left) (x right))
        (= (y left) (y right))))
 
+(defmethod manh-dist ((one point) (two point))
+  (+ (abs (- (x one) (x two)))
+     (abs (- (y one) (y two)))))
+
 
 (defclass sensor ()
   ((self-coord :initarg :self :reader self-coord)
@@ -93,7 +97,7 @@
           do (format t "iterating for x:~a y:~a~%" x to-check-y))))))
 
 (count-certainly-not-beacons "day15-test.txt")
-(count-certainly-not-beacons "day15-input.txt")
+;; (count-certainly-not-beacons "day15-input.txt")
 
 ;; well, that's just too slow
 ;; how do i rewrite it to make it faster?
@@ -112,3 +116,36 @@
 ;; nope, even if it were 5 minutes for 16mil,
 ;; so 2 minutes per 4 mil, then multiply by 4M - more than a day.
 ;; think better
+
+(defun subtract-interval (minuend subtrahend)
+  (if (not subtrahend)
+      (list  minuend)                   ; list of one interval
+      (destructuring-bind ((m-left m-right) (s-left s-right)) (list minuend subtrahend)
+        (cond
+          ((< m-right s-left)
+           (list (list m-left m-right))) ; minuend fully to the left
+          ((> m-left s-right)
+           (list (list m-left m-right))) ; minuend fully to the right
+          ((and (< m-left s-left)
+                (> m-right s-right))    ; minuend is around subtrahend
+           (list (list m-left (1- s-left))
+                 (list (1+ s-right) m-right))) ; part before and after subtrahend
+          ((and (>= m-left s-left)
+                (<= m-right s-right))   ; subtrahend consumes minuend
+           nil)
+          ((< m-left s-left) ; minuend start to the left, but not subtrahend consumes all right part
+           (list (list m-left (1- s-left)))) ; list of one interval
+          ((> m-right s-right)     ; minuend has part to the right of subtrahend
+           (list (list (1+ s-right) m-right)))))))
+
+
+(defun get-no-unknown-beacons-x-interval (line-y scanner)
+  (let* ((y-dist (abs (- line-y (y (self-coord scanner)))))
+         (x-slack (- (covered-dist scanner) y-dist))
+         (x-sc (x (self-coord scanner))))
+    (when (>= x-slack 0)
+      (list (- x-sc x-slack) (+ x-sc x-slack)))))
+
+(defun subtract-from-all (intervals subtrahend)
+  (mapcan (lambda (interval) (subtract-interval interval subtrahend))
+          intervals))