93 lines
2.5 KiB
Python
93 lines
2.5 KiB
Python
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import aocd
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from enum import Enum, nonmember
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import collections
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class Direction(Enum):
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NORTH = (0, -1)
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NORTHEAST = (1, -1)
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EAST = (1, 0)
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SOUTHEAST = (1, 1)
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SOUTH = (0, 1)
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SOUTHWEST = (-1, 1)
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WEST = (-1, 0)
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NORTHWEST = (-1, -1)
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@nonmember
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def opposite(d):
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return Direction((d.value[0]*-1, d.value[1]*-1))
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class Letter:
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target = 'MAS'
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def __init__(self, char, x, y, grid):
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self.char = char
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self.x = x
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self.y = y
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self.grid = grid
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def neighbour_coords(self, direction):
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return (self.x + direction.value[0], self.y + direction.value[1])
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def neighbour(self, direction):
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return self.grid[self.neighbour_coords(direction)]
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def is_center(self):
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"""Return whether this letter is in the center of the target pattern"""
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if self.char != self.target[1]:
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return False
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corners = (
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Direction.NORTHWEST,
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Direction.NORTHEAST,
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Direction.SOUTHWEST,
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Direction.SOUTHEAST,
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)
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return sum(self.neighbour(d)._is_nth_position(0, Direction.opposite(d)) for d in corners) == 2
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def _is_nth_position(self, n, direction):
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"""
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Return number of times this letter is the nth letter of the target word
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in the given direction
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"""
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# Must be the correct letter
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if self.char != self.target[n]:
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return False
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# Return True if it's the last letter
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if n == len(self.target) - 1:
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return True
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# Return False if there are no more letter in this direction
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if (next_letter := self.neighbour(direction)) is None:
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return False
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# Ask the next letter
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return next_letter._is_nth_position(n+1, direction)
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def parse(data):
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"""
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Parse string into grid, return all possible first letters of XMAS
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"""
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grid = collections.defaultdict(lambda: Letter(None, None, None, None)) # Null letters
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a_list = []
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for y, r in enumerate(data.split('\n')):
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for x, c in enumerate(r):
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grid[(x, y)] = Letter(c, x, y, grid)
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if c == 'A':
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a_list.append(grid[(x, y)])
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return a_list
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def solve(data):
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a_list = parse(data)
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return sum(a.is_center() for a in a_list)
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if __name__ == '__main__':
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solution = solve(aocd.get_data(year=2024, day=4))
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print(solution)
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aocd.submit(solution, year=2024, day=4, part='b')
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