From 31eb702de776f387da8436ac623caa8cd12d4dfb Mon Sep 17 00:00:00 2001
From: Marijn Doeve <marijn@doeve.me>
Date: Thu, 9 Dec 2021 20:28:28 +0100
Subject: [PATCH] Finally

---
 09/9.py | 76 +++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 61 insertions(+), 15 deletions(-)

diff --git a/09/9.py b/09/9.py
index 4c01da3..42a74df 100644
--- a/09/9.py
+++ b/09/9.py
@@ -1,25 +1,27 @@
-from pprint import pprint
-import numpy as np
 import sys
+import matplotlib.pyplot as plt
+import numpy as np
 
-np.set_printoptions(
-    threshold=sys.maxsize,
-    # linewidth=1000,
-)
+from collections import defaultdict
+from typing import Optional
 
 
-def is_low_point(grid: np.ndarray, y: int, x: int) -> bool:
-    current = grid[y, x]
-
-    indexies = [
+def indeces(y, x):
+    return [
         (y - 1, x),  # N
         (y, x + 1),  # E
         (y + 1, x),  # S
         (y, x - 1),  # W
     ]
 
-    for index in indexies:
+
+def is_low_point(grid: np.ndarray, y: int, x: int) -> bool:
+    current = grid[y, x]
+
+    for index in indeces(y, x):
         try:
+            if index[0] < 0 or index[1] < 0:
+                raise IndexError
             if grid[index] <= current:
                 return False
         except IndexError:
@@ -28,19 +30,60 @@ def is_low_point(grid: np.ndarray, y: int, x: int) -> bool:
     return True
 
 
+def lowest_neighbour(grid: np.ndarray, y: int, x: int) -> Optional[tuple[int, int]]:
+    lowest = grid[y, x]
+    point = None
+
+    for index in indeces(y, x):
+        try:
+            if index[0] < 0 or index[1] < 0:
+                raise IndexError
+
+            if (new := grid[index]) < lowest:
+                lowest = new
+                point = index
+        except IndexError:
+            pass
+
+    return point
+
+
+def heatmap(grid):
+    plt.imshow(grid, cmap="Greys", interpolation="nearest")
+    # plt.savefig("heat.png")
+    plt.show()
+
+
 def part_one(grid: np.ndarray):
     low_points = np.empty_like(grid, dtype=bool)
 
     for point in np.ndindex(grid.shape):
         low_points[point] = is_low_point(grid, *point)
 
-    # print(str(grid).replace(" ", ""))
-    # print(str(low_points).replace(" True", "o").replace("False", ".").replace(" ", ""))
-    # print(grid[low_points] + 1)
-
     return sum(grid[low_points] + 1)
 
 
+def part_two(grid: np.ndarray):
+    smoke_direction = np.empty_like(grid, dtype=tuple)
+
+    for point in np.ndindex(grid.shape):
+        smoke_direction[point] = lowest_neighbour(grid, *point)
+
+    basins = defaultdict(int)
+
+    for starting_point, height in np.ndenumerate(grid):
+        if height == 9:
+            continue
+
+        point = starting_point
+        while (next := smoke_direction[point]) is not None:
+            point = next
+
+        basins[point] += 1
+
+    return np.prod(sorted(basins.values(), reverse=True)[:3])
+
+
 if __name__ == "__main__":
     import sys
 
@@ -49,4 +92,7 @@ if __name__ == "__main__":
     for line in sys.stdin.readlines():
         grid_lists.append([int(x) for x in list(line.strip())])
 
+    grid = np.array(grid_lists)
+
     print("Part One:", part_one(grid))
+    print("Part Two:", part_two(grid))