81 lines
2.6 KiB
Python
81 lines
2.6 KiB
Python
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# SPDX-License-Identifier: MIT
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# Copyright (c) 2020 Akumatic
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#
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# https://adventofcode.com/2020/day/18
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def read_file() -> list:
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with open(f"{__file__.rstrip('code.py')}input.txt", "r") as f:
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return [line.strip() for line in f.readlines()]
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def evaluate(values: list, operators: list, precedence: bool) -> int:
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if not precedence: # "+" and "*" have same precedence levels
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result = int(values[0])
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for i in range(len(operators)):
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if operators[i] == "+":
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result += int(values[i+1])
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else: # operators[i] == "*"
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result *= int(values[i+1])
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else: # "+" and "*" have different precedence levels; "+" evaluated before "*"
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while True:
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try:
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idx = operators.index("+")
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values = values[:idx] + [values[idx] + values[idx+1]] + values[idx+2:]
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operators = operators[:idx] + operators[idx+1:]
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except ValueError:
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break
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result = 1
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for factor in values:
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result *= factor
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return result
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def parse(expression: str, precedence: bool = False) -> int:
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expression = expression.replace(" ", "")
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values = list()
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operators = list()
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i = 0
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while i < len(expression):
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if expression[i] == "+":
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operators.append("+")
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i += 1
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elif expression[i] == "*":
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operators.append("*")
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i += 1
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elif expression[i] == "(":
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# find correct closing bracket
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layer = 1
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j = i + 1
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while j < len(expression):
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if expression[j] == "(":
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layer += 1
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elif expression[j] == ")":
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if layer == 1:
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break
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layer -= 1
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j += 1
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# evaluate expression between brackets
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values.append(parse(expression[i+1:j], precedence))
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i += j - i + 1
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else: # numbers
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j = i
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value = 0
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while j < len(expression) and expression[j].isnumeric():
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value = value * 10 + int(expression[j])
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j += 1
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values.append(value)
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i += j - i
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return evaluate(values, operators, precedence)
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def part1(input: list) -> int:
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return sum([parse(line) for line in input])
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def part2(input: list) -> int:
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return sum([parse(line, precedence=True) for line in input])
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if __name__ == "__main__":
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input = read_file()
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print(f"Part 1: {part1(input)}")
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print(f"Part 2: {part2(input)}")
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