1 DEC

D1/main.janet

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+# (import math)
+
+# The smallest number in the left list is 1, and the smallest number in the
+# right list is 3. The distance between them is 2.
+
+(def test-input
+  [[3 4]
+   [4 3]
+   [2 5]
+   [1 3]
+   [3 9]
+   [3 3]])
+
+(defn unzip [lst]
+  (def left @[])
+  (def right @[])
+  (each [fst snd] lst
+    (array/push left fst)
+    (array/push right snd))
+  [(sorted left) (sorted right)])
+
+(def test-input-unzipped (unzip test-input))
+
+# The second-smallest number in the left list is 2, and the second-smallest
+# number in the right list is another 3. The distance between them is 1.
+
+# The third-smallest number in both lists is 3, so the distance between them is
+# 0.
+
+# The next numbers to pair up are 3 and 4, a distance of 1.
+
+# The fifth-smallest numbers in each list are 3 and 5, a distance of 2.
+
+# Finally, the largest number in the left list is 4, while the largest number in
+# the right list is 9; these are a distance 5 apart. To find the total distance
+# between the left list and the right list, add up the distances between all of
+# the pairs you found.
+
+# In the example above, this is 2 + 1 + 0 + 1 + 2 + 5, a total distance of 11!
+
+(defn distances [lst]
+  (def max-idx (min (length (lst 0))
+		    (length (lst 1))))
+  (def results @[])
+  (for idx 0 max-idx
+    (def dist (math/abs (- ((lst 0) idx)
+			   ((lst 1) idx))))
+    (array/push results dist))
+  (+ ;results))
+
+(def line-grammar
+  '{:main (sequence (capture :d+) :s+ (capture :d+)) })
+
+(def handle (file/open "input"))
+(def buffer @"")
+(def pairs @[])
+
+(while true
+  (def line (file/read handle :line))
+  (when (not line)
+    (break))
+  (def captures (peg/match line-grammar line))
+  (when captures
+    (def [fst snd] captures)
+    (array/push pairs [(scan-number fst) (scan-number snd)])))
+
+(print
+ (distances (unzip pairs)))
+
+(def [left right] (unzip pairs))
+
+(print
+ (+ ;(map (fn [entry]
+	    (def equal-to-entry?
+	      (fn [rval]
+		(= rval entry)))
+	    (* entry (count equal-to-entry? right)))
+	  left)))
+# ----

D1/prompt.md

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+You haven't even left yet and the group of Elvish Senior Historians has already
+hit a problem: their list of locations to check is currently empty. Eventually,
+someone decides that the best place to check first would be the Chief
+Historian's office.
+
+Upon pouring into the office, everyone confirms that the Chief Historian is
+indeed nowhere to be found. Instead, the Elves discover an assortment of notes
+and lists of historically significant locations! This seems to be the planning
+the Chief Historian was doing before he left. Perhaps these notes can be used
+to determine which locations to search?
+
+Throughout the Chief's office, the historically significant locations are listed
+not by name but by a unique number called the location ID. To make sure they
+don't miss anything, The Historians split into two groups, each searching the
+office and trying to create their own complete list of location IDs.
+
+There's just one problem: by holding the two lists up side by side (your puzzle
+input), it quickly becomes clear that the lists aren't very similar. Maybe you
+can help The Historians reconcile their lists?
+
+For example:
+
+```
+3   4
+4   3
+2   5
+1   3
+3   9
+3   3
+```
+
+Maybe the lists are only off by a small
+amount! To find out, pair up the numbers and measure how far apart they are.
+Pair up the smallest number in the left list with the smallest number in the
+right list, then the second-smallest left number with the second-smallest right
+number, and so on.
+
+Within each pair, figure out how far apart the two numbers are; you'll need to
+add up all of those distances. For example, if you pair up a 3 from the left
+list with a 7 from the right list, the distance apart is 4; if you pair up a 9
+with a 3, the distance apart is 6.
+
+In the example list above, the pairs and distances would be as follows:
+
+The smallest number in the left list is 1, and the smallest number in the right
+list is 3. The distance between them is 2. The second-smallest number in the
+left list is 2, and the second-smallest number in the right list is another 3.
+The distance between them is 1. The third-smallest number in both lists is 3,
+so the distance between them is 0. The next numbers to pair up are 3 and 4, a
+distance of 1. The fifth-smallest numbers in each list are 3 and 5, a distance
+of 2. Finally, the largest number in the left list is 4, while the largest
+number in the right list is 9; these are a distance 5 apart. To find the total
+distance between the left list and the right list, add up the distances between
+all of the pairs you found. In the example above, this is 2 + 1 + 0 + 1 + 2 +
+5, a total distance of 11!
+
+Your actual left and right lists contain many location IDs. What is the total
+distance between your lists?
+

D1/retrospect.md

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+1. Read the documentation !!!
+2. Actually seriously though, read it, don't just skim it.
+3. Use the best tool for the job.
+5. Debugging feels really hard; none of the debugging feel standard. I need to read the manual on how to do debugging.