_1.Breadth_first_search.py

flag=0
visited = [] # List for visited nodes.
queue = []     #Initialize a queue
graph={}

def addnode(v):
    if v in graph:
        print("present")
    else:
        graph[v]=[]
    
def addedge(v1,v2):
    if v1 not in graph:
        print (v1,"is not present")
    elif v2  not in graph:
        print (v2,"is not present")
    else:
        graph[v1].append(v2)
        graph[v2].append(v1)

def bfs(visited, graph, node, goal, flag): #function for BFS
    if(flag==0):
        visited.append(node)
        queue.append(node)
        while queue:          # Creating loop to visit each node
            m = queue.pop(0) 
            print (m, end = " ") 
            if(m==goal):
                print("Goal node Found")
                flag=1
                exit(0)
            elif(flag==0):
                for neighbour in graph[m]:
                    if neighbour not in visited:
                        visited.append(neighbour)
                        queue.append(neighbour)

# Driver Code
n=int(input("Enter the number of nodes:"))     
for i in range(1,n+1):
    print("Enter the value of node ",i)
    v=int(input())
    addnode(v)
for i in range(1,n+1):
    print("Enter the number of connections of node ",i)
    m=int(input())
    for j in range(0,m):
        x=int(input("Enter the connections:"))
        addedge(i,x)
x=int(input("Enter the goal node:"))
s=int(input("Enter the starting node:"))
print("Breadth First Search is :")
bfs(visited,graph,s,x,0)    # function calling