(3|4)+lisp files for puzzles 3 and 4

2 files changed, 126 insertions, 0 deletions

diff --git a/puzzle-3.lisp b/puzzle-3.lisp
new file mode 100644
index 0000000..dcb8bc3
--- /dev/null
+++ b/puzzle-3.lisp
@@ -0,0 +1,67 @@
+(defvar input (uiop:read-file-string "puzzle-3-input.txt"))
+
+(defun split-string-in-two (s)
+  (let ((len (length s)))
+    (list (subseq s 0 (/ len 2)) (subseq s (/ len 2)))))
+
+(defvar inputs (with-input-from-string (s input)
+                 (loop
+                   for line = (read-line s nil)
+                   until (null line)
+                   collect (split-string-in-two line))))
+
+(defun string-to-clist (str)
+  (loop for char across str collect char))
+
+(defun common-types (s1 s2)
+  (car (intersection
+        (string-to-clist s1)
+        (string-to-clist s2))))
+
+(defvar shared (mapcar (lambda (x)
+                    (destructuring-bind (s1 s2) x
+                      (common-types s1 s2)))
+                  inputs))
+
+(defun priority-map (c)
+  (if (upper-case-p c)
+      (+ 27 (- (char-code c) (char-code #\A)))
+      (+ 1 (- (char-code c) (char-code #\a)))))
+
+(defvar round-1-answer (reduce #'+ (mapcar #'priority-map shared)))
+
+;; Round 2
+
+;; Simple recursive algorithm which produces consecutive groups of 3 elements
+(defun group-by-3 (lst)
+  (if (null lst)
+      nil
+      (cons
+       (list (car lst) (car (cdr lst)) (car (cdr (cdr lst))))
+       (group-by-3 (cdr (cdr (cdr lst)))))))
+
+;; Note the use of group-by-3 here
+(defvar inputs (group-by-3
+                (with-input-from-string (s input)
+                  (loop
+                    for line = (read-line s nil)
+                    until (null line)
+                    collect line))))
+
+;; Extend intersection to three
+(defun common-types-3 (s1 s2 s3)
+  (car
+   (intersection
+    (string-to-clist s1)
+    (intersection
+     (string-to-clist s2)
+     (string-to-clist s3)))))
+
+;; Extend the destructuring bind and use of common-types-3
+(defvar shared (mapcar (lambda (x)
+                    (destructuring-bind (s1 s2 s3) x
+                      (common-types-3 s1 s2 s3)))
+                  inputs))
+
+;; Same as before
+(defvar round-2-answer (reduce #'+ (mapcar #'priority-map shared)))
diff --git a/puzzle-4.lisp b/puzzle-4.lisp
new file mode 100644
index 0000000..be842d3
--- /dev/null
+++ b/puzzle-4.lisp
@@ -0,0 +1,59 @@
+;; Example input: a-b,c-d which denotes [a,b] and [c,d]
+
+;; We want to find if [c,d] < [a,b] or vice versa (complete inclusion)
+;; and since we're working with integers, it's simply checking if the
+;; bounds are included i.e. c in [a,b] and d in [a,b]
+
+(defvar input (uiop:read-file-string "puzzle-4-input.txt"))
+
+(defun parse-bound (str)
+  "Given STR=\"a-b\" return (a b)"
+  (let* ((sep (search "-" str))
+         (first (subseq str 0 sep))
+         (second (subseq str (+ sep 1))))
+    (list (parse-integer first) (parse-integer second))))
+
+(defvar completed-parse
+  (with-input-from-string (s input)
+    (loop for line = (read-line s nil)
+          until (null line)
+          collect
+          ;; given a-b,c-d we want ((a b) (c d))
+          (let* ((sep (search "," line))
+                 (first-bound (subseq line 0 sep))
+                 (second-bound (subseq line (+ sep 1))))
+            (list (parse-bound first-bound) (parse-bound second-bound))))))
+
+(defun complete-inclusion (first-bound second-bound)
+  (destructuring-bind (a b) first-bound
+    (destructuring-bind (c d) second-bound
+      (or
+       (and
+        (>= a c) (<= a d)
+        (>= b c) (<= b d))
+       (and
+        (>= c a) (<= c b)
+        (>= d a) (<= d b))))))
+
+(defvar round-1-answer (length (remove-if #'null
+                                          (mapcar (lambda (pair)
+                                               (destructuring-bind (first second) pair
+                                                 (complete-inclusion first second)))
+                                             completed-parse))))
+
+;; Round 2: any overlap at all.  Basically just overhaul the inclusion
+;; function and then do the same answer checking.
+(defun any-inclusion (first second)
+  (destructuring-bind (a b) first
+    (destructuring-bind (c d) second
+      ;; How about doing this through negation?  [a,b] does not overlap with [c,d] at all if either b < c or a > d.
+      (not
+       (or
+        (< b c)
+        (> a d))))))
+
+(defvar round-2-answer (length (remove-if #'null
+                                          (mapcar (lambda (pair)
+                                               (destructuring-bind (first second) pair
+                                                 (any-inclusion first second)))
+                                             completed-parse))))