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https://github.com/thib8956/advent-of-code.git
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76 lines
2.5 KiB
Python
76 lines
2.5 KiB
Python
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import re
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import math
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from itertools import cycle
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def parse_input(infile):
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with open(infile) as f:
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content = f.read().rstrip()
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directions, nodes = content.split("\n\n")
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directions = directions.strip()
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nodes = nodes.split("\n")
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nodes = [n.split(" = ") for n in nodes]
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nodes = {k: re.findall(r"\w{3}", v) for k, v in nodes}
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return directions, nodes
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def part1(directions, nodes):
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iterations = 0
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current_node = "AAA"
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for d in cycle(directions):
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if current_node == "ZZZ":
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break
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iterations += 1
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if d == "L":
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current_node = nodes[current_node][0]
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else:
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current_node = nodes[current_node][1]
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print(f"Part 1: reached 'ZZZ' in {iterations} iterations")
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def part2(directions, nodes):
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current_nodes = [k for k in nodes.keys() if k.endswith("A")]
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# keep track of iterations number for each visited node
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# (the number will stop to beeing incremented once the node n_i value reached the target value 'xxZ')
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iterations = [0] * len(current_nodes)
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for d in cycle(directions):
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if all(c.endswith("Z") for c in current_nodes):
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break
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if d == "L":
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new_nodes = []
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for i, n in enumerate(current_nodes):
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if n.endswith("Z"): # end condition already reached for this node
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new_nodes.append(n)
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else:
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new_nodes.append(nodes[n][0])
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iterations[i] += 1
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current_nodes = new_nodes
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else:
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new_nodes = []
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for i, n in enumerate(current_nodes):
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if n.endswith("Z"): # end condition already reached for this node
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new_nodes.append(n)
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else:
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new_nodes.append(nodes[n][1])
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iterations[i] += 1
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current_nodes = new_nodes
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# the result is the lowest common multiple between the number of iterations
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# for each node
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result = math.lcm(*iterations)
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print(f"Part 2: reached all nodes such that 'xxZ' in {result} iterations")
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if __name__ == "__main__":
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import sys
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import os
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SCRIPTPATH = os.path.dirname(os.path.realpath(__file__))
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infile = sys.argv[1] if len(sys.argv) == 2 else "example.txt"
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directions, nodes = parse_input(os.path.join(SCRIPTPATH, infile))
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part1(directions, nodes)
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directions, nodes = parse_input(os.path.join(SCRIPTPATH, infile))
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part2(directions, nodes)
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