Fix visited-node initialization in BFS shortest distance

Author: Shubham-Padkonde

graphs/breadth_first_search_shortest_path_2.py

@@ -91,7 +91,7 @@ def bfs_shortest_path_distance(graph: dict, start, target) -> int:
     if start == target:
         return 0
     queue = deque([start])
-    visited = set(start)
+    visited = {start}
     # Keep tab on distances from `start` node.
     dist = {start: 0, target: -1}
     while queue: