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etotheipi/aoc2020_day18_p2_hack

Last active December 18, 2020 08:02
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Abusing Python to solve AoC 2020, Day 18 part 2
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aoc2020_day18_p2_hack
class ModInt:
""" An int that adds when you * and multiplies when you + """
def __init__(self, val):
self.val = val
def __mul__(self, other):
return ModInt(self.val + other.val)
def __add__(self, other):
return ModInt(self.val * other.val)
accum = 0
for expr in input_lines:
ecopy = expr[:]
# Replace all int literals in string with new class
for c in '0123456789':
ecopy = ecopy.replace(c, f'ModInt({c})')
# Swap all +/*
ecopy = ecopy.replace('*', 'X')
ecopy = ecopy.replace('+', '*')
ecopy = ecopy.replace('X', '+')
# "6*2+(2+(7*7))" has become "ModInt(6)+ModInt(2)*(ModInt(2)*(ModInt(7)+ModInt(7)))"
# Built-in eval() applies correct operator precedence
accum += eval(ecopy).val
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