186 lines
7.0 KiB
Python
186 lines
7.0 KiB
Python
import math
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# --- Day 12: Rain Risk ---
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# Your ferry made decent progress toward the island, but the storm came in
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# faster than anyone expected. The ferry needs to take evasive actions!
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# Unfortunately, the ship's navigation computer seems to be malfunctioning;
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# rather than giving a route directly to safety, it produced extremely
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# circuitous instructions. When the captain uses the PA system to ask if anyone
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# can help, you quickly volunteer.
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# The navigation instructions (your puzzle input) consists of a sequence of
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# single-character actions paired with integer input values. After staring at
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# them for a few minutes, you work out what they probably mean:
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# Action N means to move north by the given value.
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# Action S means to move south by the given value.
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# Action E means to move east by the given value.
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# Action W means to move west by the given value.
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# Action L means to turn left the given number of degrees.
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# Action R means to turn right the given number of degrees.
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# Action F means to move forward by the given value in the direction the ship is currently facing.
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# The ship starts by facing east. Only the L and R actions change the direction
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# the ship is facing. (That is, if the ship is facing east and the next
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# instruction is N10, the ship would move north 10 units, but would still move
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# east if the following action were F.)
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# For example:
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# F10
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# N3
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# F7
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# R90
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# F11
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# These instructions would be handled as follows:
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# F10 would move the ship 10 units east (because the ship starts by facing
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# east) to east 10, north 0.
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# N3 would move the ship 3 units north to east 10, north 3.
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# F7 would move the ship another 7 units east (because the ship is still
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# facing east) to east 17, north 3.
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# R90 would cause the ship to turn right by 90 degrees and face south; it
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# remains at east 17, north 3.
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# F11 would move the ship 11 units south to east 17, south 8.
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# At the end of these instructions, the ship's Manhattan distance (sum of the
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# absolute values of its east/west position and its north/south position) from
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# its starting position is 17 + 8 = 25.
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# Figure out where the navigation instructions lead. What is the Manhattan
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# distance between that location and the ship's starting position?
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with open("files/P12.txt", "r") as f:
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instructions = [line for line in f.read().strip().split("\n")]
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def part_1() -> None:
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# dirs are E, S, W, and N
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dirs = [[1, 0], [0, -1], [-1, 0], [0, 1]]
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current_pos = [0, 0]
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current_dir = 0
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for instr in instructions:
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_dir, _num = instr[:1], instr[1:]
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if _dir == "E":
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current_pos[0] += int(_num)
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elif _dir == "W":
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current_pos[0] -= int(_num)
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elif _dir == "N":
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current_pos[1] += int(_num)
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elif _dir == "S":
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current_pos[1] -= int(_num)
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elif _dir == "F":
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current_pos[0] += int(_num) * dirs[current_dir][0]
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current_pos[1] += int(_num) * dirs[current_dir][1]
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else:
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if _dir == "R":
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# rotations are clockwise
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current_dir += int(_num) // 90
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else:
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current_dir -= int(_num) // 90
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# avoid rotation overflow, just in case
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current_dir %= 4
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manhattan_distance = abs(current_pos[0]) + abs(current_pos[1])
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print(f"The Manhattan distance is {manhattan_distance}")
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# --- Part Two ---
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# Before you can give the destination to the captain, you realize that the
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# actual action meanings were printed on the back of the instructions the whole
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# time.
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# Almost all of the actions indicate how to move a waypoint which is relative
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# to the ship's position:
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# Action N means to move the waypoint north by the given value.
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# Action S means to move the waypoint south by the given value.
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# Action E means to move the waypoint east by the given value.
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# Action W means to move the waypoint west by the given value.
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# Action L means to rotate the waypoint around the ship left
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# (counter-clockwise) the given number of degrees.
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# Action R means to rotate the waypoint around the ship right (clockwise)
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# the given number of degrees.
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# Action F means to move forward to the waypoint a number of times equal to
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# the given value.
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# The waypoint starts 10 units east and 1 unit north relative to the ship. The
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# waypoint is relative to the ship; that is, if the ship moves, the waypoint
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# moves with it.
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# For example, using the same instructions as above:
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# F10 moves the ship to the waypoint 10 times (a total of 100 units east
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# and 10 units north), leaving the ship at east 100, north 10. The waypoint
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# stays 10 units east and 1 unit north of the ship.
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# N3 moves the waypoint 3 units north to 10 units east and 4 units north of
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# the ship. The ship remains at east 100, north 10.
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# F7 moves the ship to the waypoint 7 times (a total of 70 units east and
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# 28 units north), leaving the ship at east 170, north 38. The waypoint stays
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# 10 units east and 4 units north of the ship.
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# R90 rotates the waypoint around the ship clockwise 90 degrees, moving it
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# to 4 units east and 10 units south of the ship. The ship remains at east 170,
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# north 38.
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# F11 moves the ship to the waypoint 11 times (a total of 44 units east and
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# 110 units south), leaving the ship at east 214, south 72. The waypoint stays
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# 4 units east and 10 units south of the ship.
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# After these operations, the ship's Manhattan distance from its starting
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# position is 214 + 72 = 286.
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# Figure out where the navigation instructions actually lead. What is the
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# Manhattan distance between that location and the ship's starting position?
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def part_2() -> None:
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ship_pos = [0, 0]
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waypoint_pos = [10, 1]
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waypoint_dir = 0
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for instr in instructions:
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_dir, _num = instr[:1], instr[1:]
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if _dir == "E":
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waypoint_pos[0] += int(_num)
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elif _dir == "W":
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waypoint_pos[0] -= int(_num)
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elif _dir == "N":
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waypoint_pos[1] += int(_num)
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elif _dir == "S":
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waypoint_pos[1] -= int(_num)
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elif _dir == "F":
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ship_pos[0] += int(_num) * waypoint_pos[0]
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ship_pos[1] += int(_num) * waypoint_pos[1]
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else:
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if _dir == "R":
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# rotations are clockwise
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_num = str(360 - int(_num))
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waypoint_dir += int(_num)
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# avoid rotation overflow
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waypoint_dir %= 360
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# convert to radians to make life easier
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radians = math.radians(int(_num))
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waypoint_pos = [
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round(
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(waypoint_pos[0] * math.cos(radians))
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- (waypoint_pos[1] * math.sin(radians))
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),
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round(
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(waypoint_pos[0] * math.sin(radians))
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+ (waypoint_pos[1] * math.cos(radians))
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),
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]
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manhattan_distance = abs(ship_pos[0]) + abs(ship_pos[1])
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print(f"The Manhattan distance is {manhattan_distance}")
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if __name__ == "__main__":
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part_1()
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part_2()
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