Day 18
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54
2020/day18.py
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54
2020/day18.py
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import re
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import sys
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SUBEXPR = re.compile(r"\([^\(\)]+\)")
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def main():
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lines = [line.rstrip() for line in sys.stdin]
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# Part 1
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acc = 0
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for line in lines:
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while (subexprs := list(SUBEXPR.finditer(line))):
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for sub in subexprs:
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sub_text = sub.group(0)
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value = spacemath(sub_text.strip("()").split())
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line = line.replace(sub_text, str(value), 1)
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acc += spacemath(line.split())
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print("Sum:", acc)
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# Part 2
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acc = 0
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for line in lines:
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while (subexprs := list(SUBEXPR.finditer(line))):
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for sub in subexprs:
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sub_text = sub.group(0)
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value = advanced(sub_text.strip("()").split())
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line = line.replace(sub_text, str(value), 1)
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acc += advanced(line.split())
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print("Sum with advanced math:", acc)
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def spacemath(tokens):
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acc = int(tokens[0])
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for i in range(1, len(tokens) - 1, 2):
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op, rhs = tokens[i], tokens[i + 1]
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acc = (acc + int(rhs)) if op == "+" else (acc * int(rhs))
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return acc
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def advanced(tokens):
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while len(tokens) > 1: # solve additions first
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try:
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i = tokens.index("+")
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except ValueError:
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break
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simplification = int(tokens[i - 1]) + int(tokens[i + 1])
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tokens[i - 1:i + 2] = [simplification]
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return spacemath(tokens) # lazily reuse spacemath for multiplication
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if __name__ == "__main__":
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main()
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