Created shortest path using bfs (#794)

* Created shortest path using bfs

graphs/bfs-shortestpath.py

@@ -0,0 +1,43 @@
+graph = {'A': ['B', 'C', 'E'],
+         'B': ['A','D', 'E'],
+         'C': ['A', 'F', 'G'],
+         'D': ['B'],
+         'E': ['A', 'B','D'],
+         'F': ['C'],
+         'G': ['C']}
+
+def bfs_shortest_path(graph, start, goal):
+    # keep track of explored nodes
+    explored = []
+    # keep track of all the paths to be checked
+    queue = [[start]]
+ 
+    # return path if start is goal
+    if start == goal:
+        return "That was easy! Start = goal"
+ 
+    # keeps looping until all possible paths have been checked
+    while queue:
+        # pop the first path from the queue
+        path = queue.pop(0)
+        # get the last node from the path
+        node = path[-1]
+        if node not in explored:
+            neighbours = graph[node]
+            # go through all neighbour nodes, construct a new path and
+            # push it into the queue
+            for neighbour in neighbours:
+                new_path = list(path)
+                new_path.append(neighbour)
+                queue.append(new_path)
+                # return path if neighbour is goal
+                if neighbour == goal:
+                    return new_path
+ 
+            # mark node as explored
+            explored.append(node)
+ 
+    # in case there's no path between the 2 nodes
+    return "So sorry, but a connecting path doesn't exist :("
+ 
+bfs_shortest_path(graph, 'G', 'D')  # returns ['G', 'C', 'A', 'B', 'D']