aoc2022/d15.py

import lib
import math

EXAMPLE = """
Sensor at x=2, y=18: closest beacon is at x=-2, y=15
Sensor at x=9, y=16: closest beacon is at x=10, y=16
Sensor at x=13, y=2: closest beacon is at x=15, y=3
Sensor at x=12, y=14: closest beacon is at x=10, y=16
Sensor at x=10, y=20: closest beacon is at x=10, y=16
Sensor at x=14, y=17: closest beacon is at x=10, y=16
Sensor at x=8, y=7: closest beacon is at x=2, y=10
Sensor at x=2, y=0: closest beacon is at x=2, y=10
Sensor at x=0, y=11: closest beacon is at x=2, y=10
Sensor at x=20, y=14: closest beacon is at x=25, y=17
Sensor at x=17, y=20: closest beacon is at x=21, y=22
Sensor at x=16, y=7: closest beacon is at x=15, y=3
Sensor at x=14, y=3: closest beacon is at x=15, y=3
Sensor at x=20, y=1: closest beacon is at x=15, y=3
"""

def unify_ranges(ranges):
    # aaaaaaaaaaa
    #     bbbb
    #
    # aaa
    #     bbb
    #
    # aaa
    #   bbb
    ranges = sorted(ranges)
    while True:
        for i in range(len(ranges) - 1):
            a, b = ranges[i], ranges[i + 1]
            if a == b:
                del ranges[i]
                break
            elif a[0] == b[0]:
                ranges[i] = (a[0], max(a[1], b[1]))
                del ranges[i + 1]
                break
            elif a[1] == b[1]:
                ranges[i] = (min(a[0], b[0]), b[1])
                del ranges[i + 1]
                break
            elif a[0] < b[0] and a[1] > b[1]:
                del ranges[i + 1]
                break
            elif a[0] > b[0] and a[1] < b[1]:
                del ranges[i]
                break
            elif a[1] < b[0]:
                pass
            elif a[0] <= b[1] and a[1] >= b[0]:
                ranges[i] = (a[0], b[1])
                del ranges[i + 1]
                break
            else:
                raise Exception("uhoh", a, b)
        else:
            return ranges
    return ranges

def mdist(dx, dy):
    return abs(dx) + abs(dy)

def xdist(dm, dy):
    x = dm - abs(dy)
    if x <= 0:
        return 0
    return x

def solve(lines: list[str], yt):
    sensors = []
    bacons = set()
    for (i, line) in enumerate(lines):
        digits = lib.str_to_ints(line)
        sx, sy, bx, by = digits
        sm = mdist(bx - sx, by - sy)
        sensors.append([sx, sy, sm])
        bacons.add((bx, by))

    ranges = []
    for (sx, sy, sm) in sensors:
        x_range = xdist(sm, yt - sy)
        if x_range == 0:
            continue
        r = (sx - x_range, sx + x_range)
        # print(f"{sx=} {sy=} {r=}")
        ranges.append(r)

    ranges = unify_ranges(ranges)
    r = 0
    for (a, b) in ranges:
        r += b - a + 1
        for (bx, by) in list(bacons):
            if by == yt and bx >= a and bx <= b:
                r -= 1
    # 140:00 I don't know what a Manhattan distance is.
    return r

def solve2(lines: list[str], xymax):
    sensors = []
    bacons = set()
    for (i, line) in enumerate(lines):
        digits = lib.str_to_ints(line)
        sx, sy, bx, by = digits
        sm = mdist(bx - sx, by - sy)
        sensors.append([sx, sy, sm])
        bacons.add((bx, by))

    finds = []
    for yt in range(0, xymax):
        ranges = []
        for (sx, sy, sm) in sensors:
            x_range = xdist(sm, yt - sy)
            if x_range == 0:
                continue
            r = (sx - x_range, sx + x_range)
            ranges.append(r)
        ranges = unify_ranges(ranges)

        if ranges[0][0] > 0:
            raise Exception("Bacon at 0.")
        elif ranges[-1][-1] < xymax:
            raise Exception("Bacon at xymax.")

        for i in range(len(ranges) - 1):
            if ranges[i + 1][0] - ranges[i][1] > 1:
                finds.append((ranges[i][1] + 1, yt))
    if len(finds) != 1:
        raise Exception("TOO MANY FINDS")
    else:
        x, y = finds[0]
        return x * 4000000 + y
    # 10:00

def main():
    lines = lib.str_to_lines_no_empty(EXAMPLE)
    print("Example  1:", solve(lines, 10))

    lines = lib.str_to_lines_no_empty(open("i15.txt").read())
    print("Solution 1:", solve(lines, 2000000))

    lines = lib.str_to_lines_no_empty(EXAMPLE)
    print("Example  2:", solve2(lines, 20))

    lines = lib.str_to_lines_no_empty(open("i15.txt").read())
    print("Solution 2:", solve2(lines, 4000000))

if __name__ == "__main__":
    main()