Squash commit

utilities/graph_topo_sort.py

@@ -0,0 +1,21 @@
+def graph_topo_sort(num_nodes, edges):
+    from collections import deque
+    nodes, order, queue = {}, [], deque()
+    for node_id in range(num_nodes):
+        nodes[node_id] = { 'in': 0, 'out': set() }
+    for node_id, pre_id in edges:
+        nodes[node_id]['in'] += 1
+        nodes[pre_id]['out'].add(node_id)
+    for node_id in nodes.keys():
+        if nodes[node_id]['in'] == 0:
+            queue.append(node_id)
+    while len(queue):
+        node_id = queue.pop()
+        for outgoing_id in nodes[node_id]['out']:
+            nodes[outgoing_id]['in'] -= 1
+            if nodes[outgoing_id]['in'] == 0:
+                queue.append(outgoing_id)
+        order.append(node_id)
+    return order if len(order) == num_nodes else []
+
+print(graph_topo_sort(3, [[0, 1], [0, 2]]))