Python/graphs/bfs_shortest_path.py

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']