Solution to problem 18 part 2 in Python

src/2020/P18.py

@@ -98,5 +98,91 @@ def part_1() -> None:
     print(f"The result of evaluating my homework is {total}")
 
 
+# --- Part Two ---
+
+# You manage to answer the child's questions and they finish part 1 of their
+# homework, but get stuck when they reach the next section: advanced math.
+
+# Now, addition and multiplication have different precedence levels, but
+# they're not the ones you're familiar with. Instead, addition is evaluated
+# before multiplication.
+
+# For example, the steps to evaluate the expression 1 + 2 * 3 + 4 * 5 + 6 are
+# now as follows:
+
+# 1 + 2 * 3 + 4 * 5 + 6
+#   3   * 3 + 4 * 5 + 6
+#   3   *   7   * 5 + 6
+#   3   *   7   *  11
+#      21       *  11
+#          231
+
+# Here are the other examples from above:
+
+#     1 + (2 * 3) + (4 * (5 + 6)) still becomes 51.
+#     2 * 3 + (4 * 5) becomes 46.
+#     5 + (8 * 3 + 9 + 3 * 4 * 3) becomes 1445.
+#     5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4)) becomes 669060.
+#     ((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2 becomes 23340.
+
+# What do you get if you add up the results of evaluating the homework problems
+# using these new rules?
+
+
+def simplify_rules(expr) -> str:
+    while len(expr) > 1:
+        ordered_stack, hold = [], []
+        done = False
+
+        while not done and len(expr) > 0:
+            char = expr.pop()
+            if char == "+":
+                done = True
+            hold.append(char)
+
+        if not done and len(expr) == 0:
+            result = simplify(hold)
+            expr.append(result)
+        else:
+            ordered_stack.append(expr.pop())
+            for _ in range(2):
+                ordered_stack.append(hold.pop())
+
+            result = simplify(ordered_stack)
+            hold.append(result)
+
+            while len(hold) > 0:
+                expr.append(hold.pop())
+
+    return expr[0]
+
+
+def part_2() -> None:
+    total = 0
+    for line in homework:
+        line = line.replace("(", "( ")
+        line = line.replace(")", " )")
+        expr = line.split()
+
+        stack = []
+        for char in expr:
+            if char.isdigit() or char in ["+", "*", "("]:
+                stack.append(char)
+            elif char == ")":
+                ordered_stack = []
+                while stack[len(stack) - 1] != "(":
+                    ordered_stack.append(stack.pop())
+                stack.pop()
+
+                result = simplify_rules(ordered_stack)
+                stack.append(result)
+        stack.reverse()
+        result = simplify_rules(stack)
+        total += int(result)
+
+    print(f"The result of evaluating my homework is {total}")
+
+
 if __name__ == "__main__":
     part_1()
+    part_2()