Add day 12 part 1 solution

day12/input.txt

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+<x=9, y=13, z=-8>
+<x=-3, y=16, z=-17>
+<x=-4, y=11, z=-10>
+<x=0, y=-2, z=-2>

day12/py/main.py

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+import itertools
+import sys
+import re
+
+
+class Moon:
+    INPUT_REGEXP = re.compile(r'(\w)=(-?\d*)')
+
+    def __init__(self, x: int, y: int, z: int):
+        self.x = x
+        self.y = y
+        self.z = z
+        self.x_velocity = 0
+        self.y_velocity = 0
+        self.z_velocity = 0
+
+    @classmethod
+    def fromInputString(cls, input_str: str) -> 'Moon':
+        matches = re.findall(cls.INPUT_REGEXP, input_str)
+        fields = {}
+        for match in matches:
+            fields[match[0]] = int(match[1])
+
+        return cls(fields['x'], fields['y'], fields['z'])
+
+    @property
+    def potential_energy(self):
+        return abs(self.x) + abs(self.y) + abs(self.z)
+
+    @property
+    def kinetic_energy(self):
+        return abs(self.x_velocity) + abs(self.y_velocity) + abs(self.z_velocity)
+
+    # Applies gravity to this moon and other moon passed in
+    def apply_gravity(self, other: 'Moon') -> None:
+        FIELDS = {
+            'x': 'x_velocity',
+            'y': 'y_velocity',
+            'z': 'z_velocity'
+        }
+
+        for pos_field, velocity_field in FIELDS.items():
+            self_velocity = getattr(self, velocity_field)
+            other_velocity = getattr(other, velocity_field)
+            self_pos = getattr(self, pos_field)
+            other_pos = getattr(other, pos_field)
+            if self_pos > other_pos:
+                setattr(self, velocity_field, self_velocity - 1)
+                setattr(other, velocity_field, other_velocity + 1)
+            elif self_pos < other_pos:
+                setattr(self, velocity_field, self_velocity + 1)
+                setattr(other, velocity_field, other_velocity - 1)
+
+    # Update all of the positions based on the stored velocities
+    def update_position(self) -> None:
+        self.x += self.x_velocity
+        self.y += self.y_velocity
+        self.z += self.z_velocity
+
+    def __repr__(self) -> str:
+        return (f'pos=<x={self.x}, y={self.y}, z={self.z}> ' +
+                f'vel=<x={self.x_velocity}, y={self.y_velocity}, z={self.z_velocity}>')
+
+
+def part1(moons: Moon) -> int:
+    for i in range(1000):
+        for moon_1, moon_2 in itertools.combinations(moons, 2):
+            moon_1.apply_gravity(moon_2)
+        for moon in moons:
+            moon.update_position()
+
+    return sum(moon.kinetic_energy * moon.potential_energy for moon in moons)
+
+
+if __name__ == '__main__':
+    if len(sys.argv) != 2:
+        print("Usage: ./main.py in_file")
+        sys.exit(1)
+
+    with open(sys.argv[1]) as f:
+        moons = [Moon.fromInputString(line.rstrip()) for line in f if len(line.rstrip()) > 0]
+
+    print(part1(moons))

day12/sample.txt

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+<x=-1, y=0, z=2>
+<x=2, y=-10, z=-7>
+<x=4, y=-8, z=8>
+<x=3, y=5, z=-1>

day12/sample2.txt

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+<x=-8, y=-10, z=0>
+<x=5, y=5, z=10>
+<x=2, y=-7, z=3>
+<x=9, y=-8, z=-3>