Fix topological sort order

sorts/topological_sort.py

@@ -15,27 +15,53 @@
 vertices: list[str] = ["a", "b", "c", "d", "e"]
 
 
-def topological_sort(start: str, visited: list[str], sort: list[str]) -> list[str]:
-    """Perform topological sort on a directed acyclic graph."""
-    current = start
-    # add current to visited
+def _visit(
+    current: str,
+    visited: list[str],
+    post_order: list[str],
+    graph: dict[str, list[str]],
+) -> None:
+    """Visit all descendants of the current vertex using DFS."""
     visited.append(current)
-    neighbors = edges[current]
-    for neighbor in neighbors:
-        # if neighbor not in visited, visit
+    for neighbor in graph[current]:
         if neighbor not in visited:
-            sort = topological_sort(neighbor, visited, sort)
-    # if all neighbors visited add current to sort
-    sort.append(current)
-    # if all vertices haven't been visited select a new one to visit
-    if len(visited) != len(vertices):
-        for vertice in vertices:
+            _visit(neighbor, visited, post_order, graph)
+    post_order.append(current)
+
+
+def topological_sort(
+    start: str,
+    visited: list[str],
+    sort: list[str],
+    graph: dict[str, list[str]] | None = None,
+    vertices_list: list[str] | None = None,
+) -> list[str]:
+    """
+    Perform topological sort on a directed acyclic graph.
+
+    >>> result = topological_sort("a", [], [], edges, vertices)
+    >>> all(
+    ...     result.index(parent) < result.index(child)
+    ...     for parent, children in edges.items()
+    ...     for child in children
+    ... )
+    True
+    """
+    if graph is None:
+        graph = edges
+    if vertices_list is None:
+        vertices_list = list(graph)
+
+    _visit(start, visited, sort, graph)
+    if len(visited) != len(vertices_list):
+        for vertice in vertices_list:
             if vertice not in visited:
-                sort = topological_sort(vertice, visited, sort)
-    # return sort
+                _visit(vertice, visited, sort, graph)
+    sort.reverse()
     return sort
 
 
 if __name__ == "__main__":
-    sort = topological_sort("a", [], [])
-    print(sort)
+    result = topological_sort("a", [], [], edges, vertices)
+    assert result == ["a", "b", "e", "d", "c"]
+    print(result)