From 58ee9f48c4c90352bccdb1cc88d7b9ef923f9216 Mon Sep 17 00:00:00 2001
From: bd <bdunahu@operationnull.com>
Date: Mon, 10 Jun 2024 12:26:20 -0600
Subject: AoC 2015.3 p1+2

---
 perfectly-spherical-houses-in-a-vacuum/README.org  | 41 +++++++++++
 perfectly-spherical-houses-in-a-vacuum/input.txt   |  1 +
 perfectly-spherical-houses-in-a-vacuum/main.scm    | 16 +++++
 .../pshiav-test.scm                                | 83 ++++++++++++++++++++++
 perfectly-spherical-houses-in-a-vacuum/pshiav.scm  | 54 ++++++++++++++
 5 files changed, 195 insertions(+)
 create mode 100644 perfectly-spherical-houses-in-a-vacuum/README.org
 create mode 100644 perfectly-spherical-houses-in-a-vacuum/input.txt
 create mode 100644 perfectly-spherical-houses-in-a-vacuum/main.scm
 create mode 100644 perfectly-spherical-houses-in-a-vacuum/pshiav-test.scm
 create mode 100644 perfectly-spherical-houses-in-a-vacuum/pshiav.scm

diff --git a/perfectly-spherical-houses-in-a-vacuum/README.org b/perfectly-spherical-houses-in-a-vacuum/README.org
new file mode 100644
index 0000000..39fd3d6
--- /dev/null
+++ b/perfectly-spherical-houses-in-a-vacuum/README.org
@@ -0,0 +1,41 @@
+See: https://adventofcode.com/2015/day/3
+** Part 1
+*** Purpose
+Given a list of directional arrows:
+
+#+begin_example
+^>><v
+#+end_example
+
+Determine how many unique spaces on a grid are reached.
+
+*** Method
+
+As a more creative solution, we can use closure to create an environment which keeps track of visited spaces. Say this environment contains an initial variable with this value:
+
+#+begin_example
+'((0 . 0))
+#+end_example
+
+And we translate each instruction to a different pair of values, each representing a direction.
+
+^>><v:
+
+#+begin_example
+'((0 . 1)
+  (1 . 0)
+  (1 . 0)
+  (-1 . 0)
+  (0 . -1))
+#+end_example
+
+Then simply call the procedure that is encapsulated by a local environment, and have it add the cons pair to the previous and update its internal state.
+
+Finally, we can have another procedure that returns the length of the local list.
+
+** Part 2
+*** Purpose
+The next part claims we now have two visitors. Each of them take turns receiving directions. I chose an object-like approach for part one because the original problem claimed we were tracking "Santa" visiting houses---this is a good thing, which truly shines now that we have two visitors.
+
+*** Method
+All we need to do is change the main function to create multiple visitors, store them in a list, and cycle through the list of visitors when we process instructions.
diff --git a/perfectly-spherical-houses-in-a-vacuum/input.txt b/perfectly-spherical-houses-in-a-vacuum/input.txt
new file mode 100644
index 0000000..783e28b
--- /dev/null
+++ b/perfectly-spherical-houses-in-a-vacuum/input.txt
@@ -0,0 +1 @@
+>^^v^<>v<<<v<v^>>v^^^<v<>^^><^<<^vv>>>^<<^>><vv<<v^<^^><>>><>v<><>^^<^^^<><>>vv>vv>v<<^>v<>^>v<v^<>v>><>^v<<<<v^vv^><v>v^>>>vv>v^^^<^^<>>v<^^v<>^<vv^^<^><<>^>><^<>>><><vv><>v<<<><><>v><<>^^^^v>>^>^<v<<vv^^<v<^<^>^^v^^^^^v<><^v><<><^v^>v<<>^<>^^v^<>v<v^>v>^^<vv^v><^<>^v<><^><v^><><><<<<>^vv^>^vvvvv><><^<vv^v^v>v<<^<^^v^<>^<vv><v<v^v<<v<<^^>>^^^v^>v<><^vv<<^<>v<v><><v^^><v<>^^>^^>v^>^<<<<v><v<<>v><^v>^>><v^^<^>v<vvvv<>>>>>^v^^>v<v<^<vv>^>^vv^>vv^^v<<^<^^<>v>vv^v>><>>>v^>^>^^v<>^<v<<>^vv>v^<<v>v<<><v>^vvv<v<vvv^v<vv<v^^^>v><<^<>><v^^>^v^>>^v<^<><v<>>v^<>>v<>>v^^^><^>>vvvv>^v<^><<>>^<>^>vv><v<<>>^^>v^^^><^<<^^v>v<^<<>v>^^vvv^v^>v^<>^^<>v^v>v>v<v^>vv>^^v<>v>>^<>><>v>v^<<vvvv<vvv><v^<^>^v<>>^><v>><>^<v>v<v>vv^>>vvv<>v>v<v^>>^>>v<<>^<>^<>>>^v<<<^<^v>vv^>><<><v^>^v^^^v<>^^vv><>><>>^>v^<v<>v<>>^<<^v>^^^<>^v^><>v<<v>vv^>vv<<>>><<^v^<>v<vv>>>^^<>^><<^>vv>>^<<v^^vv<>>><v>v><^<v<<>>>^^<>>^<^v><>vv^^^v>vvv>^><<>^^>^<<v^<v<^v<<>vvv<^<<>^>^v<vv<^>vvv>v>vv^<v^><>>^vv<^^^vv><^vv<v^<><v^vvv><<^>^^><v<<vv^>v<vv<v>^<>^v<<>v<v^v^>^>^>v<<^vvv<<<v>^^>^<<<<>vv>>^<>^>>>v<v>^^<v^<v<>>>vv>^^v<<>>>^^v><<<v<v<^v<>^^><v<^v<<v^><><^<><v<^^v>>><v^^v<<v^><^<><<v^>><^<>v>v^<><^<v>^v^>^>^vv^>^^<<vv^>vv<^vvv<>>^^<^>v^>^>^<v^><v<v>>>v<<<><^v<<><^<vv^v^^^>v<^^<v^vvv<v<><v<vv<^vv<>vv<v^<>>vvvvv<<>^v^v>vv>>>vvv^^<^<^<><>v<v>><^v><^<<<>><<<v>^>v<>^>^v>>^<>v^<^>><<>^<v>^>^^^>^^<v>>>><>^v^v><<<<vv^<vv<>vv>v<>v^<v^>v><>>>v^<><^vvv>vv^<^<<^<^^v>^>>>v<^<^v^^<^<^>>><v>vv>^<<><>^>>v>^<<>><^<>v<>vv^^>^>vvv^v<<^<^^<vv<>^vvv<^^v^vv^>>v<^>^^<v^<>v<^<^vv>v<<vv>vv>^>vvv>>>^^>v<>^v>v^<^>>v>^^v>>>>v^<v>v<^>v<v<<>>^v<^^<v><^<>>^<<vv^>>v<<v>^v<>><^>vv<v<^>>^^<vvvvvvvvv>>>v<v<>v^<>>^vv<v^^v<<^vvv^<<^><>vv<><<>>v>vv^><>>^^v^>>v^v^><<<>>^^<^v<<^<>>>>^<^>v^><<^>v<^v<^>>^^<<<<><^<^v^v<>>^v<^<<vv^<><^^vv><v^v^v>^>>^>^vv^>^v<v^v<<vvv^><>>^v^^><>v>vv><^>>vv<vvv<<<<^<>vvv^v<v>^<v<^>^<^<v<><>v^^^^<<vv<^^vv<v>><<v^><>>><v^>^v><^>^><vv^<><^<v>><<^vv<>>v^<<v<>v><v<><><vv>^>>v^<^<v>^><>>><^><v^v<>>>^^<^>v<v>vvv<>^<<><v^^>^>>v<^v>^>v>>>vv>v>>v^^^<^<vvv^<>^>^<v^<v^v>v>^>vv>vvv<>v<^>v>^^>>^<vv^^v>v^^^^^v^vv><^<><>^>vv<^>>^vvvv^^^>^<vv>^v<<^><^^>^<>^^>^<<v<^>>>^><<^^>v^v>>^>vvvv>^^v><v>>vv><<<vv<^>v>^^^<v>v^vvv<^><<^>^<>^><<<<<v^<<vv^v>^<>v<v>^>^>><>v^v<^vv^^>vv<<v^v>vv^vvv<<<<>^v<v^^v^v>v<<v>^^<>^vv^^>^>^v^vv^>>v^vv^^<vv><<v^v^^v><vv<^vvv<vv^^<<v>v^v^^^^v<^<^>v>^>v>^vv^v^^<v<^vvvv<<<>^<^^^<^^<>^<><vv<^^<<^>>><v^vvvv>^<>>^^>v^^v^<<v^^^<<<><^<v^v^^v<v^<>v><<v<>^v>v<^><^>vv^^<vvv<^v>>v>^<><v^><^^^<v^>>vv<<<<<^<>^v^v>^vv^<>v>v<^>vv<<^vv>vv<v<><>>v>><v<^<^^>><<v^v<<^><v<^<vv<v<<vv^>^<<><^^>^<^>>^<vv>><v<<vvv<^^v^>^^<^v>^v<v<>v><v^v^<<^<><<v<<^v>v<<>>^>v>>v>>v<^<<^<^>>>v>^^^v><^>^^>>v<<>^v><v>vvv^vv<<<>vvv<<>^>>>v<v<v^<^<^>^<^>v^^v<^^<v<>v<>>^^>^v^>v<<<<^<>v^><<<v>>>><<v^<^vv>v>><>>^<<<^<^^>v<>>v<>vv<<^<<><<^>v^^^vv^>vvvv>>v>v^><<v<>vv^<<><<vvv>^>>>^<<<^<^<<v>^>v<>>v>>vv^^><<<<^^^v>><<^><v><v^^><v<<v^^v^^v>>v<><><<>^><v><^<vv>><^v<>v<vvv<>^>><v>>v<^><<v>^<>^v><^><^^<v>^><^^v^<<><>>^>v^<^v^vv<><^>vv^>v^vvv^<>>^><^<^<>^<<v^v<^v><>^v<v>>^>>^v^vv>><vv><v^^<<^v^<>^v<<>^><^>><v>>v<<<v^^vv<>^^v>>><><><<v^<<<v^<^^><v^>v^^vv<v^<>>vv^<^v<>^v>>v^v>v<^^vv><>^v<<>v^<>v^>>v>vvv<^><><^^>^vv^>>v^>^<^^<><>><<>^^^><^v^v><<<><<^v^vv>v>><^>>><v^>v<v><><v^v<>v^^>>v<<>v>v<v<v<^^<><>v^^<>>v<^v<v>v<><v<v>^<<>v>vv^^<>>^^^<>^^>^v>v>>>^v^v><v^^<><v>^^v^v<^<^^><<v<^<^<>^<>><<>^>>^>^^><v><>v<><>><<<>>>>vv>>>^>>^v<^>v^^^v<<vv>><<<^<<<>>>>>^>vv<^v^<>^<v^>^v><v>vvv<>>>^v^^^v<<<<>>^^<vv<^<^^>^<>v<^<<<>><>>v<^<>^<vvv<^<>><><<v>^^^>^^<<v<v^>^^v^>><<^vv><v>^v>>^<v>v>^^>^v>^vvv<>v^v^^<><vv>vv^>>><>v<^><v<v^<><<<>^v>^v<<<^>^>^>v^v<<><vvv<<v^^<><v>^>>><vv>><v>>v^<vv>>vv<<^v^v<<><^v<vv>>>vv<>>>>^vv>v^<>vv>v^v<v^><v<^^^^^>vv<><<vvv^<v><^<vv><^^^vv^<>^^^^<^><^<>v^<v^v<<^v<<^^<>>^<v^^>>>vv<vvv<>v<<>><^vvv^<<^^<<>>>^<>>>v^^><>><<>><v^v>>>>>><>>><v^<<vvv^>v<>>v^<>vv<><^^^^v^<<^<v^vv><<^^>v<^vvv^v>>v>^>>v>^^><<v^<>v<>vv<^v^vv><v><<vv^v>>v^>>v<^^^>^><<v<>^><>v>>>vvv<v<vv<^>>^v<v>^<^^^^^v><>v><>v^v^v<v^vv^v>vvvv<>vv<<<vv<v<<>^<^>^^v^<<>^<v><^><v<v<><<>v^<<^<><vv>v<<^v>>^v<><v>^>>^^><>v^<^<vvv^>^>^<<<<>vv>^v^v<^^^<vv>><>^^<<v<^<^^>>>v^v<<^^^<v<v<^<>^v<v><v^vv^^v^^v^^<vv<>^<><vv^<^v^<<^><<vvv>^^<^^^<^v>^>^vv><<<^v<v>vv>v<>v^v<v^>v^>>>v^v<>^v<<>^vv>v>v>v^<^>v^^<^>^^^^vv>^^><^>vv^>>^^v>><<<<^><>v<>^<v<vv^>^^><<^><v>v^>^^<^>>><>><v^v<v^<v<vv^v^<<^<vvv>>><vv<^^>>^>^><<v^<>>v>v^v^^><<>vv^v>v^<v><^<>^^<^>v>^<><<<v>^<^<^>^>^>^^v^<<^^v^^<^<>><^>v>>^^<>^^^<<<<v^>^v<^vv>^<<<v<><<v<>vv>>>v><>>><>>v<<<vv><>^v>v<^>><^><><v<>^v^>^v>^v<<><<^<>>v>^><>^>><>><^<v^><v^^<><v><^^>^v^^<>v^<v^<^v<v^^^^^v^<<^>^^^<^v><>^^<<<><<<<<^^>v^vvvv>v<>>vv<^>^v^>v<^vv^v<<><<v>v^v>^^><><^<v^>v><vv><>>><<>^vv<>v>>v<^v>>>v<v>v>v>^vv<<>^^vv<v<^v^<v<v>vv<>^<^<vv<v^<^v^^><<>^>><^v>vv^^v<<^^><<>v^^<><><v^^<v^v>^>^>^>v<^<v>^v^^>v<>vvv<^v<v^v><<v^><<^^><^<<v^v^>v<>^>v><><v>^<v<v>^<^^^>^v<<><<><>vv>v^<>v^><v^v<v><><<v>v<vv><<v>>v>^<<<>vv>>vvv>^^vv^v^^<^^<>v^^<>v>>^^>^>^>v>><^>><>>^<<>><^>v<<<<<<<^v^v<v^<v^^>^<><<v<^>v^>v^vv<<^^vv^>>>>^<>v<^v<>v<vv<^>>v^vv>vv><vv<<^>v>><vv>>>vv^<<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\ No newline at end of file
diff --git a/perfectly-spherical-houses-in-a-vacuum/main.scm b/perfectly-spherical-houses-in-a-vacuum/main.scm
new file mode 100644
index 0000000..9ce9361
--- /dev/null
+++ b/perfectly-spherical-houses-in-a-vacuum/main.scm
@@ -0,0 +1,16 @@
+;; -*- compile-command: "guile -L . -e main -s main.scm < input.txt"; -*-
+(use-modules (pshiav)
+	     ((ice-9 rdelim))
+	     (ice-9 binary-ports))
+
+
+(define (stdin-to-str)
+  (let loop ((result ""))
+    (let ((line (read-line)))
+      (if (eof-object? line)
+	  result
+	  (loop (string-append result line "\n"))))))
+
+(define (main args)
+  (display (pshiav (stdin-to-str) (string->number (cadr args))))
+  (newline))
diff --git a/perfectly-spherical-houses-in-a-vacuum/pshiav-test.scm b/perfectly-spherical-houses-in-a-vacuum/pshiav-test.scm
new file mode 100644
index 0000000..a27dec4
--- /dev/null
+++ b/perfectly-spherical-houses-in-a-vacuum/pshiav-test.scm
@@ -0,0 +1,83 @@
+;; -*- compile-command: "guile -L . pshiav-test.scm"; -*-
+(use-modules (srfi srfi-64)
+	     (pshiav))
+
+(test-begin "harness")
+
+
+(define coordinate-accumulator
+  (add-coordinates))
+
+(test-equal "don't move"
+  '((0 . 0) (0 . 0))
+  (coordinate-accumulator '(0 . 0)))
+
+(set! coordinate-accumulator
+  (add-coordinates))
+
+(test-equal "move up"
+  '((0 . 1) (0 . 0))
+  (coordinate-accumulator '(0 . 1)))
+
+(set! coordinate-accumulator
+  (add-coordinates))
+
+(test-equal "move up twice"
+  '((0 . 2) (0 . 1) (0 . 0))
+  (begin (coordinate-accumulator '(0 . 1))
+	 (coordinate-accumulator '(0 . 1))))
+
+(test-equal "up maps to +y"
+  '(0 . 1)
+  (direction->pair #\^))
+
+(test-equal "right maps to +x"
+  '(1 . 0)
+  (direction->pair #\>))
+
+(test-equal "down maps to -y"
+  '(0 . -1)
+  (direction->pair #\v))
+
+(test-equal "left maps to -x"
+  '(-1 . 0)
+  (direction->pair #\<))
+
+(test-equal "? maps to no change"
+  '(0 . 0)
+  (direction->pair #\?))
+
+(test-equal "empty input visits one place"
+  1
+  (pshiav "" 1))
+
+(test-equal "down once visits two places"
+  2
+  (pshiav "v" 1))
+
+(test-equal "down twice visits three places"
+  3
+  (pshiav "vv" 1))
+
+(test-equal "down twice, up once visits three places"
+  3
+  (pshiav "vv^" 1))
+
+(test-equal "up down visits three with two visitors"
+  3
+  (pshiav "^v" 2))
+
+(test-equal "up right down left visits three with two visitors"
+  3
+  (pshiav "^>v<" 2))
+
+(test-equal "opposite instructions maximizes visits with two"
+  11
+  (pshiav "^v^v^v^v^v" 2))
+
+(test-equal "opposite instructions maximizes visits with three"
+  16
+  (pshiav "^v>^v>^v>^v>^v>" 3))
+
+
+(test-end "harness")
diff --git a/perfectly-spherical-houses-in-a-vacuum/pshiav.scm b/perfectly-spherical-houses-in-a-vacuum/pshiav.scm
new file mode 100644
index 0000000..d117cce
--- /dev/null
+++ b/perfectly-spherical-houses-in-a-vacuum/pshiav.scm
@@ -0,0 +1,54 @@
+(define-module (pshiav)
+  #:use-module (srfi srfi-1)
+  #:export (pshiav
+	    add-coordinates
+	    direction->pair))
+
+(define (pshiav str num)
+  "Given string of cardinal directions STR,
+calculates the number of visited places on
+a grid.
+
+NUM specifies the number of visitors. Will
+always be at least one."
+  (set! num (max num 1))
+  (let ((visitors (map (lambda (x)
+			 (add-coordinates))
+		       (iota num))))
+    (let loop ((i 0) (lst (map direction->pair
+			       (string->list str))))
+      (if (null? lst)
+	  (length (delete-duplicates
+		   (apply append (map (lambda (visitor)
+					(visitor '(0 . 0)))
+				      visitors))))
+	  (begin
+	    ((list-ref visitors i) (car lst))
+	    (loop (modulo (1+ i) (length visitors))
+		  (cdr lst)))))))
+
+(define (add-coordinates)
+  (let ((hist '((0 . 0))))
+    (lambda dir
+      "Given cons pair DIR, increments the previous
+position, and returns HIST, a history of visited
+positions."
+      (set! hist (cons
+		  (cons (+ (caar dir)
+			   (caar hist))
+			(+ (cdar dir)
+			   (cdar hist)))
+		  hist))
+      hist)))
+
+
+(define (direction->pair char)
+  "Given a character representing one of the four
+cardinal directions, return a pair representing
+a change in coordinates."
+  (cond
+   ((char=? char #\^) '(0 . 1))
+   ((char=? char #\>) '(1 . 0))
+   ((char=? char #\v) '(0 . -1))
+   ((char=? char #\<) '(-1 . 0))
+   (#t '(0 . 0))))
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