Solve 2021 day 7-11

2021/d9.py

@@ -0,0 +1,47 @@
+from lib import get_data, Grid2D
+from collections import deque
+
+data = get_data(__file__).strip()
+g = Grid2D(data)
+
+s = 0
+low_points = []
+for row in range(g.n_rows):
+    for col in range(g.n_cols):
+        h = int(g[(row, col)])
+        for nb in g.neighbors_ort((row, col)):
+            if int(g[nb]) <= h:
+                break
+        else:
+            low_points.append((row, col))
+            s += 1 + h
+
+print(s)
+
+basins = []
+for row, col in low_points:
+    start = None
+    visited = set()
+    queue = deque([(row, col)])
+
+    while queue:
+        vertex = queue.popleft()
+        if vertex in visited:
+            continue
+        visited.add(vertex)
+
+        neighbors = []
+        for neighbor in g.neighbors_ort(vertex):
+            if neighbor in visited:
+                continue
+
+            neighbor_height = int(g[neighbor])
+            if neighbor_height < 9:
+                queue.append(neighbor)
+
+    basins.append(len(visited))
+
+s = 1
+for x in sorted(basins)[-3:]:
+    s *= x
+print(s)