2024 day 13

2024/day13/day13.py

@@ -0,0 +1,46 @@
+def parse_machine(machine):
+    btn_a, btn_b, prize = [x.split(": ")[1].split(", ") for x in machine]
+    btn_a = [int(x.split("+")[1]) for x in btn_a]
+    btn_b = [int(x.split("+")[1]) for x in btn_b]
+    prize = [int(x.split("=")[1]) for x in prize]
+    return (btn_a, btn_b, prize)
+
+
+def solve(btn_a, btn_b, prize, offset=0):
+    a_x, a_y = btn_a
+    b_x, b_y = btn_b
+    p_x, p_y = [p + offset for p in prize]
+    # apply Cramer's rule to solve the 2x2 system
+    A = (p_x*b_y - p_y*b_x) / (a_x*b_y - a_y*b_x)
+    B = (a_x*p_y - a_y*p_x) / (a_x*b_y - a_y*b_x)
+    if A.is_integer() and B.is_integer():
+        return int(A), int(B)
+    return None, None
+
+
+def main(content):
+    part1 = 0
+    part2 = 0
+    for machine in content:
+        btn_a, btn_b, prize = parse_machine(machine)
+
+        A, B = solve(btn_a, btn_b, prize)
+        if A is not None and B is not None:
+            part1 += 3*A + B
+
+        A, B = solve(btn_a, btn_b, prize, 10000000000000)
+        if A is not None and B is not None:
+            part2 += 3*A + B
+        
+    print("Part 1: ", part1)
+    print("Part 2: ", part2)
+
+
+if __name__ == "__main__":
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    with open(infile) as f:
+        content = f.read().split("\n\n")
+        content = [x.rstrip().split("\n") for x in content]
+        main(content)
+