From 941b3572ccfe243cdc7d7ce93c108734a055fcf9 Mon Sep 17 00:00:00 2001
From: I A <ia767@nyu.edu>
Date: Thu, 15 Dec 2022 08:11:21 -0500
Subject: [PATCH] [2022][day 15] adding part 2 solution

---
 2022/AOC15.py | 95 ++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 67 insertions(+), 28 deletions(-)

diff --git a/2022/AOC15.py b/2022/AOC15.py
index 0065fed..0d8e0f0 100644
--- a/2022/AOC15.py
+++ b/2022/AOC15.py
@@ -1,57 +1,96 @@
-from typing import List, Tuple, Set
+import datetime
+from typing import List, Tuple, Set, Dict
+import parse
+from _utils import read_input, timer, Solution, Point
 
-from _utils import read_input, timer, Solution
 
+MAX_Y = 4_000_000
 
-SENSOR, BEACON = 1, -1
 
-Y = 2_000_000
-
-
-def process_input(filename: str):
+def process_input(filename: str) -> Tuple[Dict[Point, int], Set[Point]]:
     _input = read_input(filename)
 
-    import parse
-
-    grid = set()
-    empty = set()
+    sensors = {}
+    beacons = set()
     for line in _input:
         x1, y1, x2, y2 = tuple(
             parse.parse(
                 "Sensor at x={:d}, y={:d}: closest beacon is at x={:d}, y={:d}", line
             ).fixed
         )
-        grid.add((x1, y1))
-        grid.add((x2, y2))
 
-        distance = manhattan_distance((x1, y1), (x2, y2))
+        sensors[(x1, y1)] = manhattan_distance((x1, y1), (x2, y2))
+        beacons.add((x2, y2))
+    return sensors, beacons
+
+
+def manhattan_distance(t1: Point, t2: Point) -> int:
+    x1, y1 = t1
+    x2, y2 = t2
+    return abs(x1 - x2) + abs(y1 - y2)
+
+
+class Solution:
+    def merge(self, intervals: List[List[Point]]) -> List[List[Point]]:
+        intervals = sorted(intervals, key=lambda i: i[0])
+        l, r = 0, 1
+
+        while r <= len(intervals) - 1:
+            if intervals[l][0] <= intervals[r][0] <= intervals[l][1]:
+                intervals[l][0] = min(intervals[l][0], intervals[r][0])
+                intervals[l][1] = max(intervals[l][1], intervals[r][1])
+                del intervals[r]
+            else:
+                l += 1
+                r += 1
+
+        return intervals
+
+
+def check_line(sensors: Dict[Point, int], Y: int, part1: bool) -> List[List[Point]]:
+    intervals = []
+
+    for pos, distance in sensors.items():
+        x1, y1 = pos
         distance_to_y = abs(y1 - Y)
         remaining_distance = distance - distance_to_y
+
         if remaining_distance >= 0:
-            for dx in range(-remaining_distance, remaining_distance + 1):
-                empty.add((x1 + dx, Y))
+            if part1:
+                intervals.append([x1 - remaining_distance, x1 + remaining_distance])
+            else:
+                min_x = max(0, x1 - remaining_distance)
+                max_x = min(MAX_Y, x1 + remaining_distance)
+                if min_x <= MAX_Y:
+                    intervals.append([min_x, max_x])
 
-    for pos in grid:
-        if pos in empty:
-            empty.remove(pos)
-    return len(empty)
+    return Solution().merge(intervals)
 
 
-def manhattan_distance(t1, t2):
-    x1, y1 = t1
-    x2, y2 = t2
-    return abs(x1 - x2) + abs(y1 - y2)
+def part1(sensors: Dict[Point, int]):
+    intervals = check_line(sensors, 2_000_000, part1=True)
+    interval_length = intervals[0][1] - intervals[0][0]
+    return interval_length
+
+
+def part2(sensors: Dict[Point, int]):
+    for y in range(MAX_Y, 0, -1):
+        intervals = check_line(sensors, y, part1=False)
+        if len(intervals) != 1:
+            x = intervals[0][1] + 1
+            return x * MAX_Y + y
+    return 0
 
 
 @timer
 def main(filename: str) -> Solution:
-    grid = process_input(filename)
-    part_1_solution = grid
-    part_2_solution = 0
+    sensors, beacons = process_input(filename)
+    part_1_solution = part1(sensors)
+    part_2_solution = part2(sensors)
     return part_1_solution, part_2_solution
 
 
 if __name__ == "__main__":
     part_1_solution, part_2_solution = main("aoc15.txt")
     print(f"PART 1: {part_1_solution}")  # 4907780
-    print(f"PART 2: {part_2_solution}")  #
+    print(f"PART 2: {part_2_solution}")  # 13639962836448 (3409990, 2836448)