From 3abfbb53ca31c4918a713930133e83d68fe41479 Mon Sep 17 00:00:00 2001
From: efim <efim.nefedov@nordigy.ru>
Date: Sun, 25 Dec 2022 14:54:34 +0000
Subject: [PATCH] day 21, part 2 backward computation. that's hot

---
 day21-scratch.lisp | 61 +++++++++++++++++++++++++++++++++++++++++---
 day21.lisp         | 63 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 120 insertions(+), 4 deletions(-)

diff --git a/day21-scratch.lisp b/day21-scratch.lisp
index 2758f97..05bc6ba 100644
--- a/day21-scratch.lisp
+++ b/day21-scratch.lisp
@@ -53,11 +53,11 @@
 
 (eval root)
 
-(load-file-defs "day21-test.txt")
-(eval root)
+;; (load-file-defs "day21-test.txt")
+;; (eval root)
 
-(load-file-defs "day21-input.txt")
-(print (eval root))
+;; (load-file-defs "day21-input.txt")
+;; (print (eval root))
 
 ;; now. things are different.
 ;; HUMN is my input
@@ -80,3 +80,56 @@
 ;; and then what?
 ;;
 ;; let's skip for now?
+
+;; or, alternatively. i could save HUMN num disregard
+;; defparameter with HUMN to be used as HUMN =
+;; and then what? root
+;; but then i'd need to reverse all the other operations, hm
+;; or, maybe i could join into flat expression?
+;; and then what? i macroexpand?
+;;
+;; now. i had an idea. i could have additional symbols,
+;; also pointing to quoted computations
+;; but these would be `back-ptdq`
+;; for line 'lgvd: ljgn * ptdq'
+;; make two? for each
+;;
+;; ptdq: humn - dvpt
+;; back-humn = ptdq + dvpt
+;; but one of these wouldn't be possible to forward eval, so it would be back-ptdq + dvpt
+;; and on
+;; root: pppw + sjmn
+;; two would be created back-pppw = - eval sjmn and vice versa
+;; this should work?
+
+;; sure, let's try?
+;; so we'd do what?
+;; same for forward eval?
+;; and two for back-monkey
+
+(back-symbol 'hello)
+
+
+(intern (format nil "BACK-~a" 'yo))
+;; and i need reverse of the operands?
+
+(reverse-operation '+)
+(line-to-quoted-operation-2 "dbpl: 5")
+(line-to-quoted-operation-2 "pppw: cczh / lfqf")
+(line-to-quoted-operation-2 "lgvd: ljgn * ptdq")
+(line-to-quoted-operation-2 "drzm: hmdt - zczc")
+(line-to-quoted-operation-2 "cczh: sllz + lgvd")
+(line-to-quoted-operation-2 "root: pppw + sjmn")
+
+
+;; i think it's done? let's try to eval all of this?
+;; but i also need root back-computation.
+;; for each operant that they are equal to forward calculation of another
+
+;; (load-file-defs-2 "day21-test.txt")
+;; (eval root)
+;; (eval back-humn)                        ; 301. cool
+
+;; (load-file-defs-2 "day21-input.txt")
+;; (print (eval back-humn))
+;; 3715799488132
diff --git a/day21.lisp b/day21.lisp
index f653d35..96864a0 100644
--- a/day21.lisp
+++ b/day21.lisp
@@ -33,3 +33,66 @@
   for line in (uiop:read-file-lines filename)
   for definition = (line-to-quoted-operation line)
   do (eval definition)))
+
+(defun reverse-operation (op)
+  (case op
+    ('*  '/)
+    ('/  '*)
+    ('+ '-)
+    ('- '+)))
+
+(defun back-symbol (symb)
+  (intern (format nil "BACK-~a" symb)))
+
+;; adding BACK-symbol computations.
+(defun line-to-quoted-operation-2 (line)
+  (let* ((words (ppcre:split " " (ppcre:regex-replace ":" line "")))
+         (symbols (mapcar #'parse-integer-or-symbol words)))
+    (cond
+      ((= 4 (length symbols))
+       ;; with operation
+       (destructuring-bind (name operand1 op operand2)
+           symbols
+         (if (eq name 'ROOT)
+             `(progn (defparameter ,(back-symbol operand1) '(eval ,operand2))
+                      (defparameter ,(back-symbol operand2) '(eval ,operand1)))
+             (let ((forward-calc
+                     `(defparameter ,name '(,op (eval ,operand1) (eval ,operand2))))
+                   (backward-calc
+                     (case op
+                       ('+ `((defparameter
+                                 ,(back-symbol operand1)
+                               '(- (eval ,(back-symbol name)) (eval ,operand2)))
+                             (defparameter
+                                 ,(back-symbol operand2)
+                               '(- (eval ,(back-symbol name)) (eval ,operand1)))))
+                       ('- `((defparameter
+                                 ,(back-symbol operand1)
+                               '(+ (eval ,(back-symbol name)) (eval ,operand2)))
+                             (defparameter
+                                 ,(back-symbol operand2)
+                               '(- (eval ,operand1) (eval ,(back-symbol name))))))
+                       (t `((defparameter
+                                ,(back-symbol operand1)
+                              '(,(reverse-operation op) (eval ,(back-symbol name)) (eval ,operand2)))
+                            (defparameter
+                                ,(back-symbol operand2)
+                              '(,(reverse-operation op) (eval ,(back-symbol name)) (eval ,operand1)))))
+                       )))
+               `(progn
+                  ,forward-calc
+                  ,@backward-calc
+                  ;; (defparameter ,(innern (format t "BACK~a" name) ))
+                  )))))
+
+      ((= 2 (length symbols))
+       ;; just number
+       (destructuring-bind (name value)
+           symbols
+         `(defparameter ,name ,value))))))
+
+(defun load-file-defs-2 (filename)
+  (loop
+  for line in (uiop:read-file-lines filename)
+  for definitions = (line-to-quoted-operation-2 line)
+  do (eval definitions)))