From 8612d41d12a3bbc19c4cf1406c76c275108c6228 Mon Sep 17 00:00:00 2001
From: Correl Roush <croush@coredial.com>
Date: Wed, 9 Dec 2015 13:35:00 -0500
Subject: [PATCH] Day 2: I Was Told There Would Be No Math

---
 advent-of-code.org | 1088 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 1088 insertions(+)

diff --git a/advent-of-code.org b/advent-of-code.org
index 180e510..ede0ed9 100644
--- a/advent-of-code.org
+++ b/advent-of-code.org
@@ -4,6 +4,10 @@
 #+PROPERTY: header-args :cache yes
 #+DRAWERS: HIDDEN
 
+#+BEGIN_SRC emacs-lisp :exports results :results silent
+  (require 'ert) ; Require ert for unit tests
+#+END_SRC
+
 * Day 1: Not Quite Lisp
 
 Santa was hoping for a white Christmas, but his weather machine's
@@ -102,3 +106,1087 @@ What is the position of the character that causes Santa to first enter the basem
 #+RESULTS[048e5b88e35ca21b8be15e5cffaa117c4e1eca45]: 1.2-solution
 : 1795
 
+* Day 2: I Was Told There Would Be No Math
+
+The elves are running low on wrapping paper, and so they need to
+submit an order for more. They have a list of the dimensions (length
+l, width w, and height h) of each present, and only want to order
+exactly as much as they need.
+
+Fortunately, every present is a box (a perfect [[https://en.wikipedia.org/wiki/Cuboid#Rectangular_cuboid][right rectangular
+prism]]), which makes calculating the required wrapping paper for each
+gift a little easier: find the surface area of the box, which is
+=2*l*w + 2*w*h + 2*h*l=. The elves also need a little extra paper for
+each present: the area of the smallest side.
+
+For example:
+
+- A present with dimensions 2x3x4 requires 2*6 + 2*12 + 2*8 = 52
+  square feet of wrapping paper plus 6 square feet of slack, for a
+  total of 58 square feet.
+- A present with dimensions 1x1x10 requires 2*1 + 2*10 + 2*10 = 42
+  square feet of wrapping paper plus 1 square foot of slack, for a
+  total of 43 square feet.
+
+All numbers in the elves' list are in feet. How many total *square
+feet of wrapping paper* should they order?
+
+----------------------------------------------------------------------
+
+:HIDDEN:
+#+name: 2-input
+#+BEGIN_EXAMPLE
+  20x3x11
+  15x27x5
+  6x29x7
+  30x15x9
+  19x29x21
+  10x4x15
+  1x26x4
+  1x5x18
+  10x15x23
+  10x14x20
+  3x5x18
+  29x23x30
+  7x4x10
+  22x24x29
+  30x1x2
+  19x2x5
+  11x9x22
+  23x15x10
+  11x11x10
+  30x28x5
+  22x5x4
+  6x26x20
+  16x12x30
+  10x20x5
+  25x14x24
+  16x17x22
+  11x28x26
+  1x11x10
+  1x24x15
+  13x17x21
+  30x3x13
+  20x25x17
+  22x12x5
+  22x20x24
+  9x2x14
+  6x18x8
+  27x28x24
+  11x17x1
+  1x4x12
+  5x20x13
+  24x23x23
+  22x1x25
+  18x19x5
+  5x23x13
+  8x16x4
+  20x21x9
+  1x7x11
+  8x30x17
+  3x30x9
+  6x16x18
+  22x25x27
+  9x20x26
+  16x21x23
+  5x24x17
+  15x17x15
+  26x15x10
+  22x16x3
+  20x24x24
+  8x18x10
+  23x19x16
+  1x21x24
+  23x23x9
+  14x20x6
+  25x5x5
+  16x3x1
+  29x29x20
+  11x4x26
+  10x23x24
+  29x25x16
+  27x27x22
+  9x7x22
+  6x21x18
+  25x11x19
+  14x13x3
+  15x28x17
+  14x3x12
+  29x8x19
+  30x14x20
+  20x23x4
+  8x16x5
+  4x11x18
+  20x8x24
+  21x13x21
+  14x26x29
+  27x4x17
+  27x4x25
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+  23x24x11
+  29x22x5
+  30x20x6
+  23x2x10
+  11x4x7
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+  10x20x19
+  8x20x22
+  5x29x22
+  16x13x2
+  2x11x14
+  6x12x4
+  3x13x6
+  16x5x18
+  25x3x28
+  21x1x5
+  20x16x19
+  28x30x27
+  26x7x18
+  25x27x24
+  11x19x7
+  21x19x17
+  2x12x27
+  20x5x14
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+  6x24x8
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+  21x8x1
+  28x19x21
+  1x14x16
+  18x2x9
+  29x28x10
+  22x26x27
+  18x26x23
+  22x24x2
+  28x26x1
+  27x29x12
+  30x13x11
+  1x25x5
+  13x30x18
+  3x13x22
+  22x10x11
+  2x7x7
+  18x17x8
+  9x22x26
+  30x18x16
+  10x2x3
+  7x27x13
+  3x20x16
+  9x21x16
+  1x18x15
+  21x30x30
+  4x25x23
+  3x11x7
+  5x6x12
+  27x1x20
+  13x15x24
+  23x29x2
+  13x5x24
+  22x16x15
+  28x14x3
+  29x24x9
+  2x20x4
+  30x10x4
+  23x7x20
+  22x12x21
+  3x19x11
+  4x28x28
+  5x4x7
+  28x12x25
+  2x16x26
+  23x20x7
+  5x21x29
+  9x21x16
+  9x6x10
+  9x6x4
+  24x14x29
+  28x11x6
+  10x22x1
+  21x30x20
+  13x17x8
+  2x25x24
+  19x21x3
+  28x8x14
+  6x29x28
+  27x10x28
+  30x11x12
+  17x2x10
+  14x19x17
+  2x11x4
+  26x1x2
+  13x4x4
+  23x20x18
+  2x17x21
+  28x7x15
+  3x3x27
+  24x17x30
+  28x28x20
+  21x5x29
+  13x12x19
+  24x29x29
+  19x10x6
+  19x12x14
+  21x4x17
+  27x16x1
+  4x17x30
+  23x23x18
+  23x15x27
+  26x2x11
+  12x8x8
+  15x23x26
+  30x17x15
+  17x17x15
+  24x4x30
+  9x9x10
+  14x25x20
+  25x11x19
+  20x7x1
+  9x21x3
+  7x19x9
+  10x6x19
+  26x12x30
+  21x9x20
+  15x11x6
+  30x21x9
+  10x18x17
+  22x9x8
+  8x30x26
+  28x12x27
+  17x17x7
+  11x13x8
+  5x3x21
+  24x1x29
+  1x28x2
+  18x28x10
+  8x29x14
+  26x26x27
+  17x10x25
+  22x30x3
+  27x9x13
+  21x21x4
+  30x29x16
+  22x7x20
+  24x10x2
+  16x29x17
+  28x15x17
+  19x19x22
+  9x8x6
+  26x23x24
+  25x4x27
+  16x12x2
+  11x6x18
+  19x14x8
+  9x29x13
+  23x30x19
+  10x16x1
+  4x21x28
+  23x25x25
+  19x9x16
+  30x11x12
+  24x3x9
+  28x19x4
+  18x12x9
+  7x1x25
+  28x7x1
+  24x3x12
+  30x24x22
+  27x24x26
+  9x30x30
+  29x10x8
+  4x6x18
+  10x1x15
+  10x4x26
+  23x20x16
+  6x3x14
+  30x8x16
+  25x14x20
+  11x9x3
+  15x23x25
+  8x30x22
+  22x19x18
+  25x1x12
+  27x25x7
+  25x23x3
+  13x20x8
+  5x30x7
+  18x19x27
+  20x23x3
+  1x17x21
+  21x21x27
+  13x1x24
+  7x30x20
+  21x9x18
+  23x26x6
+  22x9x29
+  17x6x21
+  28x28x29
+  19x25x26
+  9x27x21
+  5x26x8
+  11x19x1
+  10x1x18
+  29x4x8
+  21x2x22
+  14x12x8
+#+END_EXAMPLE
+:END:
+
+#+name: 2-solution
+#+BEGIN_SRC emacs-lisp :var input=2-input :exports both
+  (defun day2/surface-area (w h l)
+    "Calculate the surface area of a box."
+    (+ (* 2 l w)
+       (* 2 w h)
+       (* 2 h l)))
+
+  (defun day2/slack (w h l)
+    "Find the area of the smallest side of a box.
+
+  The smallest side is the side with the smallest area."
+    (min (* l w)
+         (* w h)
+         (* h l)))
+
+  (defun day2/wrapping-paper (w h l)
+    "Find the area of wrapping paper needed to wrap a box."
+    (+ (day2/surface-area w h l)
+       (day2/slack w h l)))
+
+  (ert-deftest day2/wrapping-paper ()
+    (should (eq 58 (day2/wrapping-paper 2 3 4)))
+    (should (eq 43 (day2/wrapping-paper 1 1 10))))
+
+  (defun day2/parse-dimensions (dimension-string)
+    "Parse a string representing the dimensions of a box separated
+  by the character 'x' into a list of integers."
+    (seq-map #'string-to-int
+             (split-string dimension-string "x")))
+
+  (defun day2/sum-list (input)
+    (seq-reduce
+     #'+
+     (seq-map (lambda (dimension-string)
+                (let ((dimensions (day2/parse-dimensions dimension-string)))
+                  (eval (cons 'day2/wrapping-paper dimensions))))
+              (split-string input))
+     0))
+
+  (ert-deftest day2/sum-list ()
+    (let ((test-data (string-join '("2x3x4" "1x1x10") "\n")))
+      (should (eq (+ 58 43)
+                  (day2/sum-list test-data)))))
+
+  (day2/sum-list input)
+#+END_SRC
+
+#+RESULTS[f343fb2890e11ccbcc408d25b441e9a808073e1f]: 2-solution
+: 1606483
+