My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add 2022/15
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+89
2022/day15.py
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2022/day15.py
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import sys
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import fileinput
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from utils import parse_nums, Point, NE, SE, SW, NW
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# How far to the closest beacon?
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manhattan = {}
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sensors = set()
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beacons = set()
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min_x = 1e9
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max_x = -1e9
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# Parse input
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for line in fileinput.input():
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sx, sy, bx, by = parse_nums(line)
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min_x = min(min_x, sx)
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max_x = max(max_x, sx)
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s = Point(sx, sy)
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b = Point(bx, by)
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sensors.add(s)
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beacons.add(b)
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manhattan[s] = s.dist_manhattan(b)
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# Part 1
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TARGET_Y = 2000000
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part_1 = 0
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# Only consider the sensors whose area could possibly overlap with the given row.
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close_sensors = set(s for s in sensors if s.y - manhattan[s] <= TARGET_Y <= s.y + manhattan[s])
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# Compute the intervals created by the sensor areas along this row.
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intervals = []
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for s in close_sensors:
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vertical_delta = abs(s.y - TARGET_Y)
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half_chord = manhattan[s] - vertical_delta
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intervals.append((s.x - half_chord, s.x + half_chord))
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# Merge the intervals to de-duplicate overlaps.
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intervals.sort()
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merged_intervals = []
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merged = set()
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for i, (a, b) in enumerate(intervals):
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if i in merged:
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continue
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end = b
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for j, (c, d) in enumerate(intervals):
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if i == j:
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continue
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if a <= c <= end:
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end = max(end, d)
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merged.add(j)
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merged_intervals.append((a, end))
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# Answer is the sum of merged intervals minus any beacons in that row.
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part_1 = sum(b - a + 1 for a, b in merged_intervals)
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part_1 -= sum(1 for b in beacons if b.y == TARGET_Y)
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print("Part 1:", part_1)
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# Part 2
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MIN_BEACON = 0
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MAX_BEACON = 4000000
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def gen_outskirts():
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"""Yields the set of points outside-neighbouring the perimeter of all sensors."""
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for s in sensors:
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d = manhattan[s] + 1
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p = Point(s.x - d, s.y)
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for move in [NE, SE, SW, NW]:
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for _ in range(d):
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p += move
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if MIN_BEACON <= p.x <= MAX_BEACON and MIN_BEACON <= p.y <= MAX_BEACON:
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yield p
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# Check all outskirt positions for whether it could be the undetected beacon.
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for p in gen_outskirts():
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for s in sensors:
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if p.dist_manhattan(s) <= manhattan[s]:
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break
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else:
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tuning_freq = p.x * 4000000 + p.y
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print("Part 2:", tuning_freq)
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break
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