day 3: strings as sets, loop

day3-rucksack-reorganisation.lisp

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+;; rucksack has 2 compartments
+;; items have types
+;; for each type there's 1 compartment where the item must go
+;; elf put exactly 1 item into wrong compartment for each rucksack
+;; item type is identified by letters a .. z A .. Z case sensitive
+;; first half exactly is items in first compartment, second half of chars - items in second compartment
+
+;;; find item type that appears in both compartments for each rucksack
+;; translate then item type into priority a .. z -> 1 .. 26 ; A .. Z -> 27 .. 52
+;; return sum of all priorities
+
+;;; ok. how to start solving that?
+
+(setq test-line "jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL")
+;; i need to find char that appears in the first half and in the second half.
+;; i could split the line in two, convert to list and use set diff function
+(setq half-length (/ (length test-line) 2))
+(intersection
+ (coerce (subseq test-line 0 half-length) 'list)
+ (coerce (subseq test-line half-length) 'list))
+
+;; and now char to int,
+(- (char-int #\a) (- (char-int #\a) 1))
+(- (char-int #\z) (- (char-int #\a) 1))
+(- (char-int #\A) (- (char-int #\A) 27))
+(- (char-int #\Z) (- (char-int #\A) 27))
+(lower-case-p #\z)
+(lower-case-p #\A)
+
+(defun get-char-priority (ch)
+  (if (lower-case-p ch) (- (char-int ch) (- (char-int #\a) 1))
+      (- (char-int ch) (- (char-int #\A) 27))))
+(get-char-priority #\a)
+(get-char-priority #\z)
+(get-char-priority #\A)
+(get-char-priority #\L)
+(get-char-priority #\Z)
+
+(let* ((test-line  "jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL")
+       (first-compartment (coerce (subseq test-line 0 half-length) 'list))
+       (second-compartment (coerce (subseq test-line half-length) 'list))
+       (the-misplaced-item-type (intersection first-compartment second-compartment)))
+  (get-char-priority (car the-misplaced-item-type))) ; in real life I'd need more defensiveness here, CAR woudn't be guaranteed
+
+(defun get-rucksack-misplaced-item-priority (rucksack-as-string)
+  (let* ((test-line rucksack-as-string)
+         (half-length (/ (length test-line) 2))
+         (first-compartment (coerce (subseq test-line 0 half-length)
+                                    'list))
+         (second-compartment (coerce (subseq test-line half-length)
+                                     'list))
+         (the-misplaced-item-type (intersection first-compartment second-compartment)))
+    (get-char-priority (car the-misplaced-item-type)))
+                                        ; in real life I'd need more defensiveness here, CAR woudn't be guaranteed
+  )
+
+(get-rucksack-misplaced-item-priority "jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL")
+(get-rucksack-misplaced-item-priority "PmmdzqPrVvPwwTWBwg")
+;; again I'm making mistakes by referring to the globally visible symbols inside of the functions. so bad.
+;; maybe i'd want to use something like "make-symbol" as recommended in the part on macro?
+
+;; now the funciton seems to work, need to iterate over input file, call it for each line and sum
+(defun count-priories-in-file (filename)
+  (let ((running-sum 0))
+    (with-open-file (in filename)
+      (loop
+        for line = (read-line in nil nil)
+        while line
+        do (incf running-sum
+                 (get-rucksack-misplaced-item-priority line))
+        finally (return running-sum)))))
+(count-priories-in-file "day3-input.txt")
+(count-priories-in-file "day3-test-input.txt")
+
+;;; so, now different task for same input:
+;; considering lines in groups of 3, what is their common char (group identification badge)
+;; then map to priorities and sum
+;; that should be a very similar program.
+;; but how can i configure loop to give me 3 lines at a time?
+
+(defun get-three-rucksacks-id-badge (r1 r2 r3)
+  (let* ((r1 (coerce r1 'list))
+         (r2 (coerce r2 'list))
+         (r3 (coerce r3 'list))
+         (badge-type-char (intersection (intersection r1 r2) r3)))
+    (get-char-priority (car badge-type-char)))
+                                        ; in real life I'd need more defensiveness here, CAR woudn't be guaranteed
+  )
+
+(get-three-rucksacks-id-badge "vJrwpWtwJgWrhcsFMMfFFhFp" "jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL" "PmmdzqPrVvPwwTWBwg")
+
+(defun count-id-badges-in-file (filename)
+  (let ((running-sum 0))
+    (with-open-file (in filename)
+      (loop
+        for line1 = (read-line in nil nil)
+        for line2 = (read-line in nil nil)
+        for line3 = (read-line in nil nil)
+        while line1
+        do (incf running-sum
+                 (get-three-rucksacks-id-badge line1 line2 line3))
+        finally (return running-sum)))))
+(count-id-badges-in-file "day3-test-input.txt")
+(count-id-badges-in-file "day3-input.txt")
+
+;; surely there's a better way to use loop?
+;; or maybe a good introduction into how to use it?
+;; the documentation site doesn't give examples =C