Return immediately if edge starts and finishes in the same node

TaskB05/run.py

@@ -26,6 +26,9 @@ def dfs(graph, start):
     while stack:
         edge = stack.pop()
         #print('Current edge: {edge}'.format(edge = edge))
+        #return immediately if cycle is detected
+        if edge[0] == edge[2]:
+            return [-1]
         if edge not in visited:
             visited.add(edge)
             children = set()
@@ -37,7 +40,7 @@ def dfs(graph, start):
             return [-1]
     return visited
     
-
+# load atand format from stdin
 for line in sys.stdin:
     line = line.replace('\n', '')
     move = atandt_desc_pattern.match(line)