1 files changed, 63 insertions, 0 deletions
diff --git a/2023/23/part2.py b/2023/23/part2.py
new file mode 100644
index 0000000..54e0bbe
--- /dev/null
+++ b/2023/23/part2.py
@@ -0,0 +1,63 @@
+L = [l.strip() for y, l in enumerate(open("input").readlines())]
+
+G = {}
+for y in range(1, len(L) - 1):
+    for x in range(1, len(L[0]) - 1):
+        if L[y][x] == "#":
+            continue
+        if L[y - 1][x] != "#":
+            if (y - 1, x) not in G:
+                G[(y - 1, x)] = set()
+            if (y, x) not in G:
+                G[(y, x)] = set()
+            G[(y - 1, x)].add((y, x, 1))
+            G[(y, x)].add((y - 1, x, 1))
+        if L[y][x - 1] != "#":
+            if (y, x - 1) not in G:
+                G[(y, x - 1)] = set()
+            if (y, x) not in G:
+                G[(y, x)] = set()
+            G[(y, x - 1)].add((y, x, 1))
+            G[(y, x)].add((y, x - 1, 1))
+
+# compress graph
+done = False
+while not done:
+    done = True
+    for (y, x), ns in G.items():
+        if len(ns) != 2:
+            continue
+        n1, n2 = ns
+        G[n1[:2]].add((n2[0], n2[1], n1[2] + n2[2]))
+        G[n2[:2]].add((n1[0], n1[1], n1[2] + n2[2]))
+        G[n1[:2]].remove((y, x, n1[2]))
+        G[n2[:2]].remove((y, x, n2[2]))
+        del G[(y, x)]
+
+        done = False
+        break
+
+
+def dfs(y, x):
+    end = list(G.keys())[-1]
+    ps = []
+    st = []
+    st.append((y, x, 1, set(), 1))
+    while st:
+        y, x, l, v, p = st.pop()
+        v.add((y, x))
+        ns = G[(y, x)]
+        for n in ns:
+            if n[:2] in v:
+                continue
+
+            np = p + n[2]
+            st.append((*n, set(v), np))
+
+            if n[:2] == end[:2]:  # reached end
+                ps.append(np)
+
+    print(max(p for p in ps))
+
+
+dfs(0, 1)