```
"""Topological Sort."""
edges = {"a": ["c", "b"], "b": ["d", "e"], "c": [], "d": [], "e": []}
vertices = ["a", "b", "c", "d", "e"]
def topological_sort(start, visited, sort):
"""Perform topolical sort on a directed acyclic graph."""
current = start
visited.append(current)
neighbors = edges[current]
for neighbor in neighbors:
if neighbor not in visited:
sort = topological_sort(neighbor, visited, sort)
sort.append(current)
if len(visited) != len(vertices):
for vertice in vertices:
if vertice not in visited:
sort = topological_sort(vertice, visited, sort)
return sort
if __name__ == "__main__":
sort = topological_sort("a", [], [])
print(sort)
```