Advent of Code 2023: Day 1
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Refer to the previous post about AoC, and to the git repository with my solutions in Python 3.
Link to Day #1 puzzle.
The first part is straightforward: extract the first and last digit from each line and sum them.
Part two gets trickier: we need to handle spelled-out digits like “one”, “two”, etc. The naive approach of replacing spellings with digits fails for overlapping cases like “eightwothree” which should yield 83, not 23.
The solution: find the leftmost and rightmost match among all digit spellings and numeric digits, then combine them.
python
#!/usr/bin/env python3
import sys
def get_calibration_value(line: str) -> int:
"""
Extract the first and the last digit from the string, and return a number
composed by them, in that order.
'1abc2' -> 12
"""
digits = [c for c in line if c.isdigit()]
return int(digits[0] + digits[-1])
SPELLINGS = {
# 'zero': '0', # not in the problem statement
'one': '1',
'two': '2',
'three': '3',
'four': '4',
'five': '5',
'six': '6',
'seven': '7',
'eight': '8',
'nine': '9',
}
# This attempt is incorrect because of the following test case:
# eightwothree -> eigh23 -> 23
# Whereas it should have been 83.
def get_calibration_value_with_spellings_attempt_1(line: str) -> int:
for spelling, digit in SPELLINGS.items():
line = line.replace(spelling, digit)
return get_calibration_value(line)
def get_calibration_value_with_spellings(line: str) -> int:
targets = set(list(SPELLINGS.keys()) + list(SPELLINGS.values()))
# from the left
indices = {}
for target in targets:
index = line.find(target)
if index != -1:
indices[target] = index
[target_min, _] = min(list(indices.items()), key=lambda x: x[1])
# from the right
indices = {}
for target in targets:
index = line.rfind(target)
if index != -1:
indices[target] = index
[target_max, _] = max(list(indices.items()), key=lambda x: x[1])
if target_min in SPELLINGS:
target_min = SPELLINGS[target_min]
if target_max in SPELLINGS:
target_max = SPELLINGS[target_max]
return int(target_min + target_max)
def main():
with open(sys.argv[1]) as input:
lines = input.read().splitlines()
# Part I
print(sum([get_calibration_value(line) for line in lines]))
# Part II
print(sum([get_calibration_value_with_spellings(line) for line in lines]))
if __name__ == '__main__':
main()