Day 10 Part 2 (works w/o errors but takes ages and result is wrong)

day10.py

@@ -3,13 +3,14 @@
 # https://adventofcode.com/2025/day/10
 
 from itertools import combinations, product
+from sympy import symbols, Matrix, solve_linear_system
 
 f = open("day10input.txt", "r")
 
 # regular input
-#input = f.readlines()
+input = f.readlines()
 # testinput
-input = "[.##.] (3) (1,3) (2) (2,3) (0,2) (0,1) {3,5,4,7}\n[...#.] (0,2,3,4) (2,3) (0,4) (0,1,2) (1,2,3,4) {7,5,12,7,2}\n[.###.#] (0,1,2,3,4) (0,3,4) (0,1,2,4,5) (1,2) {10,11,11,5,10,5}".split("\n")
+#input = "[.##.] (3) (1,3) (2) (2,3) (0,2) (0,1) {3,5,4,7}\n[...#.] (0,2,3,4) (2,3) (0,4) (0,1,2) (1,2,3,4) {7,5,12,7,2}\n[.###.#] (0,1,2,3,4) (0,3,4) (0,1,2,4,5) (1,2) {10,11,11,5,10,5}".split("\n")
 
 machines = []
 
@@ -56,33 +57,57 @@ def part1_bfs(m):
   return None
 
 
-# PART 2 IS NOT WORKING YET
-def part2_bfs(m):
-  l = len(m["j"])
-  switches = ["{0:b}".format(n).zfill(l) for n in m["s"]]
+def part2(m):
+  switches = [list(map(int, list("{0:b}".format(switch).zfill(len(m["j"]))))) for switch in m["s"]]
+  joltages = m["j"] 
 
-  steps = 1
-  
-  while True:
-    print(f"{steps=}")
-    # check if current step no yields a solution
-    for c in list(product(switches, repeat=steps)):
-#      print(f"{c=}")
-      j = []
-      for i in range(l):
-        j.append(sum([int(s[i]) for s in c]))
-      
-#      print(f"{j}\t{m['j']}")
-      if j == m["j"]:
-        print(f"Success with combo {i} and step count of {steps}")
-        return steps
-  
-    steps += 1
-  return None
+  # define sympy symbols and equations
+  x = symbols(f"x:{len(switches)}", integer=True)
+  system = Matrix([[switch[j] for switch in switches] + [joltages[j]] for j in range(len(joltages))])
+  print(f"Equation system to solve: {system}")
 
+  # solve system with sympy
+  solutions = solve_linear_system(system, *x)
+  print(f"Solutions: {solutions}")
   
-  
+  # isolate free variables
+  free_vars = [var for var in x if var not in solutions.keys()]
+  print(f"{free_vars=}")
 
-print_machines(machines)
-print(sum(list(map(part1_bfs, machines))))
-#print(sum(list(map(part2_bfs, machines))))
+  # find smallest solution
+  smallest_sum = None
+
+  # loop over the cartesian product of sensible numbers for button presses times the number of free variables 
+  for lv in product(range(max(joltages)), repeat=len(free_vars)):
+#    print(f"{lv=}")
+    current_sum = sum(lv)
+    for v in solutions.values():
+      for i in range(len(lv)):
+        v = v.subs(free_vars[i], lv[i])
+#      print(f"{v=}")
+      if v < 0:
+#        print(f"negative button press number for {lv=} -> skipping")
+        current_sum = -1
+        break
+      current_sum += v
+    if current_sum < 0:
+      continue
+#    print(f"-> {current_sum=}")
+    
+    # check current sum
+    if not current_sum.is_Integer:
+      continue
+    elif not smallest_sum or current_sum < smallest_sum: 
+      smallest_sum = current_sum
+  
+  print(f"Smallest number of presses found: {smallest_sum}")
+  return smallest_sum
+
+
+#print_machines(machines)
+#print(sum(list(map(part1_bfs, machines))))bin
+steps = 0
+for machine in machines:
+  steps += part2(machine)
+  print(f"current total step number: {steps}")
+print(f"final total step number: {steps}")