Merge pull request #88 from zach-wild/topological_sort

Add topological_sort.py

sorts/topological_sort.py

@@ -0,0 +1,32 @@
+#     a
+#    / \
+#   b  c
+#  / \
+# d  e
+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
+    # add current to visited
+    visited.append(current)
+    neighbors = edges[current]
+    for neighbor in neighbors:
+        # if neighbor not in visited, visit
+        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:
+            if vertice not in visited:
+                sort = topological_sort(vertice, visited, sort)
+    # return sort
+    return sort
+
+
+sort = topological_sort('a', [], [])
+print(sort)