My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add 2025/07
+54
+54
2025/day07.py
+54
2025/day07.py
···
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import fileinput
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from functools import cache
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def bfs(start):
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"""Returns the number of splits from `start`."""
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splits = 0
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horizon = [start]
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seen = set()
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while horizon:
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p = horizon.pop()
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if p in seen:
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continue
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if p not in BOARD:
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continue
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seen.add(p)
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x, y = p
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if BOARD[p] == '^':
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splits += 1
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horizon.append((x - 1, y))
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horizon.append((x + 1, y))
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else:
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horizon.append((x, y + 1))
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return splits
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@cache
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def dp(pos):
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"""Returns the number of ways a tachyon travels from x, y"""
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x, y = pos
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if pos not in BOARD:
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return 1
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if BOARD[pos] == '^':
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return dp((x - 1, y)) + dp((x + 1, y))
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return dp((x, y + 1))
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# Parse problem input.
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BOARD = {}
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START = None
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for y, line in enumerate(fileinput.input()):
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for x, c in enumerate(line.strip()):
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BOARD[x, y] = c
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if c == 'S':
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START = (x, y)
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# Solve problem.
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print("Part 1:", bfs(START))
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print("Part 2:", dp(START))