Add solution for day 4

day4/part1.py

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+"""
+--- Day 4: Camp Cleanup ---
+
+Space needs to be cleared before the last supplies can be unloaded from
+the ships, and so several Elves have been assigned the job of cleaning
+up sections of the camp. Every section has a unique ID number, and each
+Elf is assigned a range of section IDs.
+
+However, as some of the Elves compare their section assignments with
+each other, they've noticed that many of the assignments overlap. To
+try to quickly find overlaps and reduce duplicated effort, the Elves
+pair up and make a big list of the section assignments for each pair
+(your puzzle input).
+
+For example, consider the following list of section assignment pairs:
+
+2-4,6-8
+2-3,4-5
+5-7,7-9
+2-8,3-7
+6-6,4-6
+2-6,4-8
+
+For the first few pairs, this list means:
+
+- Within the first pair of Elves, the first Elf was assigned sections
+  2-4 (sections 2, 3, and 4), while the second Elf was assigned
+  sections 6-8 (sections 6, 7, 8).
+- The Elves in the second pair were each assigned two sections.
+- The Elves in the third pair were each assigned three sections: one
+  got sections 5, 6, and 7, while the other also got 7, plus 8 and 9.
+
+This example list uses single-digit section IDs to make it easier to
+draw; your actual list might contain larger numbers. Visually, these
+pairs of section assignments look like this:
+
+.234.....  2-4
+.....678.  6-8
+
+.23......  2-3
+...45....  4-5
+
+....567..  5-7
+......789  7-9
+
+.2345678.  2-8
+..34567..  3-7
+
+.....6...  6-6
+...456...  4-6
+
+.23456...  2-6
+...45678.  4-8
+
+Some of the pairs have noticed that one of their assignments fully
+contains the other. For example, 2-8 fully contains 3-7, and 6-6 is
+fully contained by 4-6. In pairs where one assignment fully contains
+the other, one Elf in the pair would be exclusively cleaning sections
+their partner will already be cleaning, so these seem like the most in
+need of reconsideration. In this example, there are 2 such pairs.
+
+In how many assignment pairs does one range fully contain the other?
+"""
+
+
+def main():
+    num_fully_contained = 0
+
+    with open("input.txt", "r", encoding="utf-8") as f:
+        for line in f:
+            if not line.strip():
+                continue
+
+            assignments = line.strip().split(",")
+            for index, assignment in enumerate(assignments):
+                first, last = assignment.split("-")
+                assignments[index] = {i for i in range(int(first), int(last)+1)}
+
+            if assignments[0].issubset(assignments[1]) or assignments[1].issubset(assignments[0]):
+                num_fully_contained += 1
+
+    print(f"Fully contained assignments: {num_fully_contained}")
+
+
+if __name__ == "__main__":
+    main()

day4/part2.py

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+"""
+--- Part Two ---
+
+It seems like there is still quite a bit of duplicate work planned.
+Instead, the Elves would like to know the number of pairs that overlap
+at all.
+
+In the above example, the first two pairs (2-4,6-8 and 2-3,4-5) don't
+overlap, while the remaining four pairs (5-7,7-9, 2-8,3-7, 6-6,4-6, and
+2-6,4-8) do overlap:
+
+- 5-7,7-9 overlaps in a single section, 7.
+- 2-8,3-7 overlaps all of the sections 3 through 7.
+- 6-6,4-6 overlaps in a single section, 6.
+- 2-6,4-8 overlaps in sections 4, 5, and 6.
+
+So, in this example, the number of overlapping assignment pairs is 4.
+
+In how many assignment pairs do the ranges overlap?
+"""
+
+
+def main():
+    intersecting_assignments = 0
+
+    with open("input.txt", "r", encoding="utf-8") as f:
+        for line in f:
+            if not line.strip():
+                continue
+
+            assignments = line.strip().split(",")
+            for index, assignment in enumerate(assignments):
+                first, last = assignment.split("-")
+                assignments[index] = {i for i in range(int(first), int(last)+1)}
+
+            if len(assignments[0].intersection(assignments[1])):
+                intersecting_assignments += 1
+
+    print(f"Intersecting assignments: {intersecting_assignments}")
+
+
+if __name__ == "__main__":
+    main()

day4/testinput.txt

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+2-4,6-8
+2-3,4-5
+5-7,7-9
+2-8,3-7
+6-6,4-6
+2-6,4-8