commit 750c10a661535def66674f0379ddaaf6c2ef0fde
parent 716e4b54a876be76712f390770e158d899ab5ad0
Author: Natasha Kerensikova <natgh@instinctive.eu>
Date: Fri, 8 Dec 2023 19:40:37 +0000
Add day 8 references and first attempt at a solution
Diffstat:
3 files changed, 281 insertions(+), 0 deletions(-)
diff --git a/day08.scm b/day08.scm
@@ -0,0 +1,266 @@
+; Copyright (c) 2023, Natacha Porté
+;
+; Permission to use, copy, modify, and distribute this software for any
+; purpose with or without fee is hereby granted, provided that the above
+; copyright notice and this permission notice appear in all copies.
+;
+; THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+; WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+; MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+; ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+; WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+; ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+; OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+(import (chicken io) (chicken string)
+ comparse
+ srfi-1
+ srfi-14
+ srfi-69)
+
+;;;;;;;;;;;;;;;;;
+;; Input parsing
+
+(define (as-number parser)
+ (bind (as-string parser)
+ (lambda (s)
+ (result (string->number s)))))
+
+(define spaces
+ (zero-or-more (is #\space)))
+
+(define direction
+ (in #\L #\R))
+
+(define directions
+ (sequence* ((data (one-or-more direction))
+ (_ (one-or-more (is #\newline))))
+ (result data)))
+
+(define node
+ (as-string (repeated (in char-set:letter) 3)))
+
+(define (punctuation p)
+ (sequence spaces (is p) spaces))
+
+(define network-line
+ (sequence* ((start node)
+ (_ (punctuation #\=))
+ (_ (punctuation #\())
+ (left node)
+ (_ (punctuation #\,))
+ (right node)
+ (_ (punctuation #\)))
+ (_ (is #\newline)))
+ (result (list start left right))))
+
+(define network
+ (one-or-more network-line))
+
+(define all-data
+ (sequence directions network))
+
+(define data (parse all-data (read-string)))
+(write-line (conc "Input: " data))
+
+;;;;;;;;;;;;;;;;;
+;; First Puzzle
+
+(define left-link-table
+ (alist->hash-table
+ (map (lambda (x) (cons (car x) (cadr x))) (cadr data))))
+
+(define right-link-table
+ (alist->hash-table
+ (map (lambda (x) (cons (car x) (caddr x))) (cadr data))))
+
+(define (follow-link dir node)
+ (cond ((eqv? dir #\L) (hash-table-ref left-link-table node))
+ ((eqv? dir #\R) (hash-table-ref right-link-table node))))
+
+(define (count-links-until directions start stop acc)
+; (write-line (conc "At step " acc ": " start))
+ (cond ((equal? start stop) acc)
+ ((null? directions) (count-links-until (car data) start stop acc))
+ (else (count-links-until (cdr directions)
+ (follow-link (car directions) start)
+ stop
+ (add1 acc)))))
+
+;(write-line (conc "First puzzle: " (count-links-until '() "AAA" "ZZZ" 0)))
+
+;;;;;;;;;;;;;;;;;
+;; Second Puzzle (inefficient)
+
+(define (start-node? node)
+ (equal? (substring node 2 3) "A"))
+
+(define (final-node? node)
+ (equal? (substring node 2 3) "Z"))
+
+(define (follow-directions directions node-history)
+ (if (null? directions)
+ (reverse node-history)
+ (follow-directions (cdr directions)
+ (cons
+ (follow-link (car directions) (car node-history))
+ node-history))))
+
+(define (process-history node-history end-steps steps last-node)
+ (if (null? node-history)
+ (list last-node end-steps)
+ (process-history (cdr node-history)
+ (if (final-node? (car node-history))
+ (cons steps end-steps)
+ end-steps)
+ (add1 steps)
+ (car node-history))))
+
+(define (process-node node)
+ (process-history (follow-directions (car data) (list node)) '() 0 '()))
+
+(define end-table
+ (alist->hash-table
+ (map (lambda (key) ;(write-line (conc key " -> " (process-node key)))
+ (cons key (process-node key)))
+ (hash-table-keys left-link-table))))
+
+(define (is-in? n l)
+ (cond ((null? l) #f)
+ ((= n (car l)) #t)
+ (else (is-in? n (cdr l)))))
+
+(define (intersect l1 l2)
+ (let loop ((todo l1) (acc '()))
+ (if (null? todo)
+ acc
+ (loop (cdr todo)
+ (if (is-in? (car todo) l2) (cons (car todo) acc) acc)))))
+
+(define (intersect-list l)
+ (let loop ((todo (cdr l)) (acc (car l)))
+ (if (null? todo)
+ acc
+ (loop (cdr todo) (intersect (car todo) acc)))))
+
+(define (answer-2 nodes past-cycles)
+ (write-line (conc "Cycle " past-cycles ": " nodes))
+ (let ((local-data (map (lambda (x) (hash-table-ref end-table x)) nodes)))
+ (let ((next-nodes (map car local-data))
+ (end-steps (map cadr local-data)))
+ (let ((merged-end-steps (intersect-list end-steps)))
+ (if (null? merged-end-steps)
+ (answer-2 next-nodes (add1 past-cycles))
+ (+ (* past-cycles (length (car data)))
+ (apply min merged-end-steps)))))))
+
+(define start-nodes
+ (filter start-node? (hash-table-keys left-link-table)))
+
+;(write-line (conc "Second puzzle: " (answer-2 start-nodes 0)))
+
+;;;;;;;;;;;;;;;;;
+;; Second Puzzle
+
+(define node-list
+ (hash-table-keys left-link-table))
+
+(define state-list
+ (let loop ((directions (car data))
+ (nodes node-list)
+ (acc '()))
+ (cond ((null? directions) acc)
+ ((null? nodes) (loop (cdr directions) node-list acc))
+ (else (loop directions
+ (cdr nodes)
+ (cons (cons (car nodes) directions) acc))))))
+
+(define (next-state state)
+ (let ((node (car state))
+ (cur-dir (cadr state))
+ (next-dir (cddr state)))
+ (cons (follow-link cur-dir node)
+ (if (null? next-dir) (car data) next-dir))))
+
+; state -> '(steps-to-cycle cycle-length cycle-start)
+(define state-cycle-table (make-hash-table))
+
+(define (state-cycle! state previous-steps)
+ (if (hash-table-exists? state-cycle-table state)
+ (let ((entry (hash-table-ref state-cycle-table state)))
+ (cond ((pair? entry) entry)
+ ((integer? entry) (hash-table-set! state-cycle-table state
+ (list 0 (- previous-steps entry) state))
+ (state-cycle! (next-state state)
+ (add1 previous-steps)))))
+ (begin
+ (hash-table-set! state-cycle-table state previous-steps)
+ (let ((next-result
+ (state-cycle! (next-state state) (add1 previous-steps))))
+ (if (integer? (hash-table-ref state-cycle-table state))
+ (hash-table-set! state-cycle-table state
+ (cons (add1 (car next-result)) (cdr next-result))))
+ (hash-table-ref state-cycle-table state)))))
+
+; state-in-cycle -> '(cycle-length steps-to-ends-in-cycle)
+; state-out-of-cycle
+; -> '(steps-to-ends-before-cycle steps-to-cycle
+; cycle-length steps-to-ends-in-cycle)
+(define state-ends-table (make-hash-table))
+
+(define (steps-to-ends-in-cycle from-state)
+ (let loop ((state (next-state from-state))
+ (steps 1)
+ (acc (if (final-node? (car from-state)) '(0) '())))
+ (if (equal? state from-state)
+ acc
+ (loop (next-state state)
+ (add1 steps)
+ (if (final-node? (car state))
+ (cons steps acc)
+ acc)))))
+
+(define (build-entry state steps steps-to-ends-before-cycle)
+ (let ((entry (hash-table-ref state-ends-table state)))
+ (if (and (pair? entry) (= (length entry) 2))
+ (cons steps-to-ends-before-cycle (cons steps entry))
+ (build-entry (next-state state)
+ (add1 steps)
+ (if (final-node? (car state))
+ (cons steps steps-to-ends-before-cycle)
+ steps-to-ends-before-cycle)))))
+
+
+(define (state-ends! state previous-steps)
+ (if (hash-table-exists? state-ends-table state)
+ (let ((entry (hash-table-ref state-ends-table state)))
+ (cond ((pair? entry) entry)
+ ((integer? entry)
+ (hash-table-set! state-ends-table state
+ (list (- previous-steps entry)
+ (steps-to-ends-in-cycle state)))
+ (state-ends! (next-state state) (add1 previous-steps))
+ (hash-table-ref state-ends-table state))))
+ (begin
+ (hash-table-set! state-ends-table state previous-steps)
+ (let ((next-result
+ (state-ends! (next-state state) (add1 previous-steps))))
+ (if (integer? (hash-table-ref state-ends-table state))
+ (hash-table-set! state-ends-table state
+ (build-entry state 0 '())))
+ (hash-table-ref state-ends-table state)))))
+
+(define start-node-list
+ (filter start-node? node-list))
+
+(write-line (conc "Start nodes: " start-node-list))
+
+(define data-2
+ (map (lambda (node) (state-ends! (cons node (car data)) 0)) start-node-list))
+
+(let loop ((rest data-2))
+ (unless (null? rest)
+ (write-line (conc (car rest)))
+ (loop (cdr rest))))
+
+(write-line (conc "Second puzzle: " ))
diff --git a/ref/day08a.txt b/ref/day08a.txt
@@ -0,0 +1,5 @@
+LLR
+
+AAA = (BBB, BBB)
+BBB = (AAA, ZZZ)
+ZZZ = (ZZZ, ZZZ)
diff --git a/ref/day08b.txt b/ref/day08b.txt
@@ -0,0 +1,10 @@
+LR
+
+DDA = (DDB, XXX)
+DDB = (XXX, DDZ)
+DDZ = (DDB, XXX)
+EEA = (EEB, XXX)
+EEB = (EEC, EEC)
+EEC = (EEZ, EEZ)
+EEZ = (EEB, EEB)
+XXX = (XXX, XXX)
