My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add 2021/15
+55
+55
2021/day15.py
+55
2021/day15.py
···
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import fileinput
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import heapq
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from utils import Point
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def shortest_path(graph, start, end):
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"""Returns the shortest path from start to end in graph."""
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horizon = [(0, start)]
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seen = set()
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while horizon:
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depth, node = heapq.heappop(horizon)
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if node == end:
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return depth
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elif node in seen:
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continue
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seen.add(node)
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for neigh in node.neighbours_4():
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if neigh not in graph:
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continue
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heapq.heappush(horizon, (depth + graph[neigh], neigh))
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return -1
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CAVE = {}
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# Read problem input and solve part 1.
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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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CAVE[Point(x, y)] = int(c)
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WIDTH = x + 1
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HEIGHT = y + 1
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print "Part 1:", shortest_path(CAVE, Point(0, 0), Point(x, y))
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# Replicate CAVE tiles to solve part 2.
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for y in range(HEIGHT*5):
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for x in range(WIDTH*5):
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if Point(x, y) not in CAVE:
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dx = x // WIDTH
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dy = y // HEIGHT
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# Need to subtract one, take modulo, then add one because we
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# are dealing with the range 1-9, not 0-8.
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val = (CAVE[Point(x % WIDTH, y % HEIGHT)] + (dx + dy))
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CAVE[Point(x, y)] = ((val - 1) % 9) + 1
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print "Part 2:", shortest_path(CAVE, Point(0, 0), Point(x, y))