From f971917640d4472c98f642aa09ce65b4e7257faa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Anders=20Engl=C3=B6f=20Ytterstr=C3=B6m?= <yttan@fastmail.se>
Date: Tue, 9 Dec 2025 14:49:19 +0100
Subject: [PATCH] Solve 2025 day 9 pt 1

Pt 2 is almost there. Need a better flood fill
algorithm.
---
 2025-python/output/day_09.py | 95 ++++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 2025-python/output/day_09.py

diff --git a/2025-python/output/day_09.py b/2025-python/output/day_09.py
new file mode 100644
index 0000000..844d437
--- /dev/null
+++ b/2025-python/output/day_09.py
@@ -0,0 +1,95 @@
+from itertools import combinations
+
+from output import ints
+
+
+def solve(data):
+    p1 = 0
+    p2 = 0
+    A = [tuple(ints(pos)) for pos in data.splitlines()]
+
+    S = A[0]
+    V = set()
+    B = set()
+
+    while True:
+        V.add(S)
+        y, x = S
+        he = [(r, c) for r, c in A if r == y and (r, c) not in V]
+        ve = [(r, c) for r, c in A if c == x and (r, c) not in V]
+        if not he and not ve:
+            E = A[0]
+        elif he and ve:
+            E = min(min(he), min(ve))
+        elif he and not ve:
+            E = min(he)
+        else:
+            E = min(ve)
+        y2, x2 = E
+        for r in range(min(y, y2), max(y, y2) + 1):
+            for c in range(min(x, x2), max(x, x2) + 1):
+                B.add((r, c))
+        if E == A[0]:
+            break
+        S = E
+    # find out a better start for Flood fill by visualizing
+    Y = 1841
+    X = 53478
+    # or, find a way to floodfill without BFS
+    # end
+    y, x = Y, X
+    Q = [(y, x)]
+    V = V | B
+    while Q:
+        yx = Q.pop()
+        if yx in V:
+            continue
+        V.add(yx)
+        y, x = yx
+        for dy, dx in D:
+            Q.append((dy + y, dx + x))
+    for a, b in combinations(A, r=2):
+        y1, x1 = a
+        y2, x2 = b
+        x = abs(x1 - x2) + 1
+        y = abs(y1 - y2) + 1
+        p1 = max(p1, x * y)
+        if (
+            len(
+                set(
+                    [
+                        (min(y1, y2), min(x1, x2)),
+                        (min(y1, y2), max(x1, x2)),
+                        (max(y1, y2), min(x1, x2)),
+                        (max(y1, y2), max(x1, x2)),
+                    ]
+                )
+                - V
+            )
+            == 0
+        ):
+            p2 = max(p2, max(p2, x * y))
+    return p1, p2
+
+
+if __name__ == "__main__":
+    inp = """
+7,1
+11,1
+11,7
+9,7
+9,5
+2,5
+2,3
+7,3    """.strip()
+
+    with open("./input/09.txt", "r") as f:
+        inp = f.read().strip()
+
+    p1, p2 = solve(inp)
+
+    print(p1)
+    print(p2)
+
+    assert p1 == 4749838800
+    assert p2 == 1624057680