AoC 2020: day18

Signed-off-by: Ettore Dreucci <ettore.dreucci@gmail.com>

2020-python/solutions/day_18.py

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+"""AOC 2020 Day 18"""
+
+import pathlib
+import time
+
+TEST_INPUT = """1 + (2 * 3) + (4 * (5 + 6))
+2 * 3 + (4 * 5)
+5 + (8 * 3 + 9 + 3 * 4 * 3)
+5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))
+((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2"""
+
+def read_input(input_path: str) -> str:
+    """take input file path and return a str with the file's content"""
+    with open(input_path, 'r') as input_file:
+        input_data = input_file.read().strip()
+        return input_data
+
+def extract(input_data: str) -> list:
+    """take input data and return the appropriate data structure"""
+    return [exp.rstrip() for exp in input_data.split('\n')]
+
+def regular_op(stack: list, num: int) -> list:
+    """return the stack after performing a regular math operation"""
+    while stack:
+        if stack[-1] == '(':
+            break
+        operator, left_operand = stack[-1], stack[-2]
+        stack = stack[:-2]
+        if operator == '+':
+            num = left_operand + num
+        elif operator == '*':
+            num = left_operand * num
+    stack.append(num)
+    return stack
+
+def advanced_op(stack: list, num: int, sub_expr: bool) -> list:
+    """return the stack after performing an advanced math operation"""
+    if sub_expr:
+        index = -1
+        for stack_index, value in enumerate(stack):
+            if value == '(':
+                index = stack_index
+        if index != -1:
+            target = stack[index+1:]
+            stack = stack[:index]
+        else:
+            target = stack
+            stack = []
+        for value in target:
+            if value != '*':
+                num *= int(value)
+    while stack:
+        if stack[-1] in '(*':
+            break
+        operator, left_operand = stack[-1], stack[-2]
+        stack = stack[:-2]
+        if operator == '+':
+            num = left_operand + num
+    stack.append(num)
+    return stack
+
+def evaluate(expression: str, advance: bool = False) -> tuple:
+    """return the result of an expression evaluated with regular or advanced math operator precendece"""
+    stack = list()
+    index = 0
+    while index < len(expression):
+        data = expression[index]
+        if data.isdigit():
+            num = int(data)
+            if advance:
+                stack = advanced_op(stack, num, False)
+            else:
+                stack = regular_op(stack, num)
+        elif data in '*+(':
+            stack.append(data)
+        elif data == ')':
+            num = int(stack[-1])
+            if advance:
+                stack = stack[:-1]
+                stack = advanced_op(stack, num, True)
+            else:
+                stack = stack[:-2]
+                stack = regular_op(stack, num)
+        index += 1
+    if advance and len(stack) > 1:
+        stack = advanced_op(stack[:-1], int(stack[-1]), True)
+    return stack[0]
+
+def part1(entries: dict) -> int:
+    """part1 solver"""
+    result_sum = 0
+    for expression in entries:
+        result_sum += evaluate(expression)
+    return result_sum
+
+def part2(entries: tuple) -> int:
+    """part2 solver"""
+    result_sum = 0
+    for expression in entries:
+        result_sum += evaluate(expression, True)
+    return result_sum
+
+def test_input_day_18():
+    """pytest testing function"""
+    entries = extract(TEST_INPUT)
+    assert part1(entries) == 26386
+    assert part2(entries) == 693942
+
+def test_bench_day_18(benchmark):
+    """pytest-benchmark function"""
+    benchmark(main)
+
+def main():
+    """main function"""
+    input_path = str(pathlib.Path(__file__).resolve().parent.parent) + "/inputs/" + str(pathlib.Path(__file__).stem)
+    start_time = time.time()
+    input_data = read_input(input_path)
+    entries = extract(input_data)
+    print("Part 1: %d" % part1(entries))
+    print("Part 2: %d" % part2(entries))
+    end_time = time.time()
+    print("Execution time: %f" % (end_time-start_time))
+
+if __name__ == "__main__":
+    main()