Day 15

antoinebrl · antoinebrl · commit 924c90658c27 · 2022-12-15T22:20:25.000+01:00
diff --git a/day15/input.txt b/day15/input.txt
@@ -0,0 +1,29 @@
+Sensor at x=2557568, y=3759110: closest beacon is at x=2594124, y=3746832
+Sensor at x=2684200, y=1861612: closest beacon is at x=2816974, y=2000000
+Sensor at x=1003362, y=1946094: closest beacon is at x=1972523, y=2563441
+Sensor at x=2142655, y=1481541: closest beacon is at x=1932524, y=967542
+Sensor at x=2796219, y=1955744: closest beacon is at x=2816974, y=2000000
+Sensor at x=3890832, y=1818644: closest beacon is at x=3454717, y=2547103
+Sensor at x=2828842, y=1921726: closest beacon is at x=2816974, y=2000000
+Sensor at x=2065227, y=583957: closest beacon is at x=1932524, y=967542
+Sensor at x=2725784, y=2088998: closest beacon is at x=2816974, y=2000000
+Sensor at x=3574347, y=927734: closest beacon is at x=1932524, y=967542
+Sensor at x=2939312, y=2652370: closest beacon is at x=3454717, y=2547103
+Sensor at x=2495187, y=3681541: closest beacon is at x=2431306, y=3703654
+Sensor at x=2878002, y=2054681: closest beacon is at x=2816974, y=2000000
+Sensor at x=1539310, y=3235516: closest beacon is at x=1972523, y=2563441
+Sensor at x=545413, y=533006: closest beacon is at x=-538654, y=69689
+Sensor at x=1828899, y=3980292: closest beacon is at x=2431306, y=3703654
+Sensor at x=3275729, y=2937931: closest beacon is at x=3454717, y=2547103
+Sensor at x=600131, y=3861189: closest beacon is at x=2431306, y=3703654
+Sensor at x=2089895, y=28975: closest beacon is at x=1932524, y=967542
+Sensor at x=2960402, y=3942666: closest beacon is at x=2594124, y=3746832
+Sensor at x=3785083, y=3905392: closest beacon is at x=2594124, y=3746832
+Sensor at x=1721938, y=1077173: closest beacon is at x=1932524, y=967542
+Sensor at x=2515156, y=3751221: closest beacon is at x=2594124, y=3746832
+Sensor at x=2469423, y=2109095: closest beacon is at x=2816974, y=2000000
+Sensor at x=1776986, y=904092: closest beacon is at x=1932524, y=967542
+Sensor at x=2789294, y=3316115: closest beacon is at x=2594124, y=3746832
+Sensor at x=3538757, y=2695066: closest beacon is at x=3454717, y=2547103
+Sensor at x=2299738, y=2708004: closest beacon is at x=1972523, y=2563441
+Sensor at x=2388366, y=3234346: closest beacon is at x=2431306, y=3703654
diff --git a/day15/main.py b/day15/main.py
@@ -0,0 +1,52 @@
+import os
+import re
+
+def parse(filename):
+    with open(filename) as f:
+        return [[int(d) for d in re.findall("(\d+)", line)] for line in  f.readlines()]
+
+def dist_l1(pt1, pt2):
+    return abs(pt2[0] - pt1[0]) + abs(pt2[1] - pt1[1])
+
+def coverage(sensors, row):
+    ranges = []
+    for (sx, sy), r in sensors.items():
+        dx = r - abs(sy - row)  # horizontal distance to edge on a certain row
+        if dx >= 0:
+            ranges.append((sx - dx, sx + dx))
+    return ranges
+
+def find_hole(ranges):
+    highest = 0
+    for a, b in sorted(ranges):
+        if a <= highest + 1:
+            highest = max(highest, b)
+        else:
+            return a 
+    return -1
+
+def part1(sensors, row):
+    ranges = coverage(sensors, row)
+    # assuming no hole on the row
+    a = min([a for a, b in ranges])
+    b = max([b for a, b in ranges])
+    return b - a
+
+def part2(sensors, limit):
+    for row in reversed(range(limit + 1)):
+        ranges = coverage(sensors, row)
+        col = find_hole(ranges)
+        if col > 0:
+            return col * 4_000_000 + row
+
+
+if __name__ == "__main__":
+    input_file = os.path.join(os.path.dirname(__file__),  "input.txt")
+    signal = parse(input_file)
+    sensors = {(sx, sy): dist_l1((sx, sy), (bx, by)) for sx, sy, bx, by in signal}
+
+    solution1 = part1(sensors, row=2_000_000)
+    print(f"part 1 - solution : {solution1}")
+
+    solution2 = part2(sensors, limit=4_000_000)
+    print(f"part 2 - solution : {solution2}")
