Question

Given breadth first search function as below. Write a bfs_new(a_tree, start, goal), which does the following. We store one additional dictionary variable, called parent, to store the parent of each node. In the beginning, set parent = { start: 'NOBODY'}. Each time that a node is expanded, we add one entry in parent for each of its children. The input goal is the name of a node; if bfs_new reaches the node called goal, then the search is terminated, and the program should print out the path from the goal node to the start node, by using the data stored in parent.

def bfs_tree(a_tree, start):

open_nodes = [start]

path = []

while len(open_nodes) > 0:

vertex = open_nodes.pop(0)​# pop(0) deletes and returns the first item

if vertex in path:

continue

path.append(vertex)​​# append adds element to end of path

for neighbor in a_tree[vertex]:

open_nodes.append(neighbor)

return path

Answer 1

bfs_new:

def bfs_new(atree, start,goal):

               open_nodes = [start]

               path = []

               parent = {start: 'NOBODY}             #parent dictionary

               while len(open_nodes)>0 and vertex!=goal:  #loops till goal isnt reached

                              vertex = open_nodes.pop(0)

                              if vertex not in path: #if vertex is never explored

                                             path.append(vertex)

                                             for neighbor in open_nodes[vertex]:

                                                            path.append(vertex)

                                                            if neighbor not in parent:               #if neighbour is not explored

                                                                           parent[neighbor] = vertex     #set vertex as parent of neighbor