Update function to handle edge cases

2023/24/part 1 solution.py

@@ -0,0 +1,51 @@
+with open(r'advent_of_code\2023\24\input.txt', 'r') as file:
+    input_data = file.read()
+
+test_input = '''19, 13, 30 @ -2,  1, -2
+18, 19, 22 @ -1, -1, -2
+20, 25, 34 @ -2, -2, -4
+12, 31, 28 @ -1, -2, -1
+20, 19, 15 @  1, -5, -3'''
+
+#input_data = test_input
+input_lines = input_data.split('\n')
+
+class Hailstone:
+    def __init__(self, start_x, start_y, start_z, velocity_x, velocity_y, velocity_z):
+        self.start_x = start_x
+        self.start_y = start_y
+        self.start_z = start_z
+        self.velocity_x = velocity_x
+        self.velocity_y = velocity_y
+        self.velocity_z = velocity_z
+        
+        self.a = velocity_y
+        self.b = -velocity_x
+        self.c = velocity_y * start_x - velocity_x * start_y
+    
+    def __repr__(self):
+        return "Hailstone{" + f"a={self.a}, b={self.b}, c={self.c}" + "}"
+
+# Parse input lines into Hailstone objects
+hailstones = [Hailstone(*map(int, line.replace("@", ",").split(","))) for line in input_lines]
+
+total_intersections = 0
+
+# Check each pair of hailstones for intersection
+for i, hailstone1 in enumerate(hailstones):
+    for hailstone2 in hailstones[:i]:
+        a1, b1, c1 = hailstone1.a, hailstone1.b, hailstone1.c
+        a2, b2, c2 = hailstone2.a, hailstone2.b, hailstone2.c
+        # If lines are parallel, they do not intersect
+        if a1 * b2 == b1 * a2:
+            continue
+        # Calculate intersection point
+        x = (c1 * b2 - c2 * b1) / (a1 * b2 - a2 * b1)
+        y = (c2 * a1 - c1 * a2) / (a1 * b2 - a2 * b1)
+        # Check if intersection point is within bounds
+        if 200000000000000 <= x <= 400000000000000 and 200000000000000 <= y <= 400000000000000:
+            # Check if intersection point is in the same direction as the hailstones' velocities
+            if all((x - hs.start_x) * hs.velocity_x >= 0 and (y - hs.start_y) * hs.velocity_y >= 0 for hs in (hailstone1, hailstone2)):
+                total_intersections += 1
+
+print(total_intersections)

2023/24/part 2 solution.py

@@ -0,0 +1,32 @@
+import sympy
+
+with open(r'advent_of_code\2023\24\input.txt', 'r') as file:
+    input_data = file.read()
+
+test_input_data = '''19, 13, 30 @ -2,  1, -2
+18, 19, 22 @ -1, -1, -2
+20, 25, 34 @ -2, -2, -4
+12, 31, 28 @ -1, -2, -1
+20, 19, 15 @  1, -5, -3'''
+
+#input_data = test_input_data
+input_lines = input_data.split('\n')
+
+hailstones = [tuple(map(int, line.replace("@", ",").split(","))) for line in input_lines]
+
+x_ref, y_ref, z_ref, vx_ref, vy_ref, vz_ref = sympy.symbols("x_ref, y_ref, z_ref, vx_ref, vy_ref, vz_ref")
+
+equations = []
+
+for i, (start_x, start_y, start_z, velocity_x, velocity_y, velocity_z) in enumerate(hailstones):
+    equations.append((x_ref - start_x) * (velocity_y - vy_ref) - (y_ref - start_y) * (velocity_x - vx_ref))
+    equations.append((y_ref - start_y) * (velocity_z - vz_ref) - (z_ref - start_z) * (velocity_y - vy_ref))
+    if i < 2:
+        continue
+    solutions = [solution for solution in sympy.solve(equations) if all(value % 1 == 0 for value in solution.values())]
+    if len(solutions) == 1:
+        break
+    
+final_solution = solutions[0]
+
+print(final_solution[x_ref] + final_solution[y_ref] + final_solution[z_ref])