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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?
+