From cb0c3d651ec7f3f0c0dc8ffb9768ec1e86f5d2d3 Mon Sep 17 00:00:00 2001
From: Brendan Chen <me@bchen.dev>
Date: Mon, 7 Sep 2026 15:50:59 -0700
Subject: [PATCH] Revert "Remove solution; revert later after going over the
 topic"

This reverts commit 8d50900eaa999e1cd7c6eb2eca5b6527d9a413e8.
---
 .../2026.08.27/topological_sort_solution.py   | 47 +++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 notes-and-examples/2026.08.27/topological_sort_solution.py

diff --git a/notes-and-examples/2026.08.27/topological_sort_solution.py b/notes-and-examples/2026.08.27/topological_sort_solution.py
new file mode 100644
index 0000000..e5b21c7
--- /dev/null
+++ b/notes-and-examples/2026.08.27/topological_sort_solution.py
@@ -0,0 +1,47 @@
+from collections import deque
+
+# This is a solution which uses DFS to trace the paths; there
+# are other solutions as well
+
+classes = {
+    'CPSC 230': {'CPSC 231'},
+    'CPSC 231': {'CPSC 350', 'CPSC 330'},
+    'CPSC 350': {'CPSC 380', 'CPSC 408', 'CPSC 406'},
+    'CPSC 330': {'CPSC 351'},
+    'CPSC 351': set(),
+    'ENGR 101': set(),
+    'CPSC 380': set(),
+    'CPSC 406': set(),
+    'CPSC 408': set()
+}
+
+
+def topological_sort(adjacency_list: dict[str, set[str]]):
+    result = deque()
+    visited = set()
+
+    def dfs(current: str, visited_in_traversal=None):
+        if visited_in_traversal is None:
+            visited_in_traversal = set()
+        if current in visited:
+            return
+        if current in visited_in_traversal:
+            raise ValueError("Graph has a cycle")
+
+        visited_in_traversal.add(current)
+
+        for neighbor in adjacency_list[current]:
+            dfs(neighbor, visited_in_traversal)
+
+        # to trace the reverse path, use .append
+        result.appendleft(current)
+        visited.add(current)
+
+    for node in adjacency_list.keys():
+        if node not in visited:
+            dfs(node)
+
+    return result
+
+
+print(topological_sort(classes))