Add whiteboard link for optimizing last week's assignment

This reverts commit 8d50900eaa.

assignments/python-packages/python-packages.md

@@ -0,0 +1,4 @@
+## Overview
+
+Create a program which creates a topological ordering of Python packages.
+See this [starter template](https://gitea.bchen.dev/brendan/python-packages-starter)

notes-and-examples/2026.08.27/overview.md

@@ -0,0 +1,5 @@
+## Overview
+
+We'll go over exercise 2 from [last week](../2026.08.20/overview.md), as well as
+a new topic: [topological sort](./topological_sort.md). Try to complete the 
+exercise from the document.

notes-and-examples/2026.08.27/topological_sort.md

@@ -0,0 +1,32 @@
+## Class ordering
+
+These are some classes for Chapman University, for
+the [computer science program](https://catalog.chapman.edu/preview_program.php?catoid=33&poid=6408&print).
+
+![An ordering of classes for Chapman University.](./classes.png)
+
+This is a *directed acyclic graph*, or DAG.
+
+- Directed: edges point from one node to another, not necessarily the other way around
+- Acyclic: there are no *cycles* in the graph
+
+We say that a class is a *prerequisite* or a *dependency* of another class
+if we need to take it before that other class. So, we need to take CPSC 230
+before CPSC 231, for example.
+
+Could you come up with something like this for your school?
+
+## The algorithm
+
+If you were to come up with a list of classes, such that the list of classes
+is in the order which you need to take them, what would that look like?
+
+This order is what we're trying to achieve with the topological sort
+algorithm. Note that there can be multiple correct solutions.
+
+By the way, [here is a link to the whiteboard](https://excalidraw.com/#json=69478-DnuxlMCcyaOkazP,I_-nOWaO9m0wJkAFfqt9JA).
+
+## The exercise
+
+Let's write the algorithm. First, test it against the Chapman classes, then
+put in your classes and see how it fares against that.

notes-and-examples/2026.08.27/topological_sort.py

@@ -15,7 +15,7 @@ classes = {
 }
 
 def topological_sort(adjacency_list: dict[str, set[str]]):
-    # return the sorted ordering
+    # return the sorted ordering ['CPSC 230', 'ENGR 101', 'CPSC 231', ...]
     return []
 
 print(topological_sort(classes))

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))

notes-and-examples/2026.09.04/overview.md

@@ -0,0 +1,7 @@
+## Overview
+
+We will go over the exercise from last week and start on [Python Packages](https://gitea.bchen.dev/brendan/python-packages-starter),
+a new assignment. For reference, this assignment is also in the Assignments section.
+
+Whiteboard for optimizing last week's assignment: https://excalidraw.com/#json=rd-1CkdxA2AMpQsiVOQkY,t7-KayQW3DntCDkXVktEJQ
+