bfs pseudocode python code example

Example 1: breadth first traversal python program

class Graph:
    def __init__(self):
        # dictionary containing keys that map to the corresponding vertex object
        self.vertices = {}
 
    def add_vertex(self, key):
        """Add a vertex with the given key to the graph."""
        vertex = Vertex(key)
        self.vertices[key] = vertex
 
    def get_vertex(self, key):
        """Return vertex object with the corresponding key."""
        return self.vertices[key]
 
    def __contains__(self, key):
        return key in self.vertices
 
    def add_edge(self, src_key, dest_key, weight=1):
        """Add edge from src_key to dest_key with given weight."""
        self.vertices[src_key].add_neighbour(self.vertices[dest_key], weight)
 
    def does_edge_exist(self, src_key, dest_key):
        """Return True if there is an edge from src_key to dest_key."""
        return self.vertices[src_key].does_it_point_to(self.vertices[dest_key])
 
    def __iter__(self):
        return iter(self.vertices.values())
 
 
class Vertex:
    def __init__(self, key):
        self.key = key
        self.points_to = {}
 
    def get_key(self):
        """Return key corresponding to this vertex object."""
        return self.key
 
    def add_neighbour(self, dest, weight):
        """Make this vertex point to dest with given edge weight."""
        self.points_to[dest] = weight
 
    def get_neighbours(self):
        """Return all vertices pointed to by this vertex."""
        return self.points_to.keys()
 
    def get_weight(self, dest):
        """Get weight of edge from this vertex to dest."""
        return self.points_to[dest]
 
    def does_it_point_to(self, dest):
        """Return True if this vertex points to dest."""
        return dest in self.points_to
 
 
class Queue:
    def __init__(self):
        self.items = []
 
    def is_empty(self):
        return self.items == []
 
    def enqueue(self, data):
        self.items.append(data)
 
    def dequeue(self):
        return self.items.pop(0)
 
 
def display_bfs(vertex):
    """Display BFS Traversal starting at vertex."""
    visited = set()
    q = Queue()
    q.enqueue(vertex)
    visited.add(vertex)
    while not q.is_empty():
        current = q.dequeue()
        print(current.get_key(), end=' ')
        for dest in current.get_neighbours():
            if dest not in visited:
                visited.add(dest)
                q.enqueue(dest)
 
 
g = Graph()
print('Menu')
print('add vertex <key>')
print('add edge <src> <dest>')
print('bfs <vertex key>')
print('display')
print('quit')
 
while True:
    do = input('What would you like to do? ').split()
 
    operation = do[0]
    if operation == 'add':
        suboperation = do[1]
        if suboperation == 'vertex':
            key = int(do[2])
            if key not in g:
                g.add_vertex(key)
            else:
                print('Vertex already exists.')
        elif suboperation == 'edge':
            src = int(do[2])
            dest = int(do[3])
            if src not in g:
                print('Vertex {} does not exist.'.format(src))
            elif dest not in g:
                print('Vertex {} does not exist.'.format(dest))
            else:
                if not g.does_edge_exist(src, dest):
                    g.add_edge(src, dest)
                else:
                    print('Edge already exists.')
 
    elif operation == 'bfs':
        key = int(do[1])
        print('Breadth-first Traversal: ', end='')
        vertex = g.get_vertex(key)
        display_bfs(vertex)
        print()
 
    elif operation == 'display':
        print('Vertices: ', end='')
        for v in g:
            print(v.get_key(), end=' ')
        print()
 
        print('Edges: ')
        for v in g:
            for dest in v.get_neighbours():
                w = v.get_weight(dest)
                print('(src={}, dest={}, weight={}) '.format(v.get_key(),
                                                             dest.get_key(), w))
        print()
 
    elif operation == 'quit':
        break

Example 2: BFS AND DFS IN C

#include<stdio.h>
#include<stdlib.h>
 
#define MAX 100  
 
#define initial 1
#define waiting 2
#define visited 3
 
int n;    
int adj[MAX][MAX];
int state[MAX]; 
void create_graph();
void BF_Traversal();
void BFS(int v);
 
int queue[MAX], front = -1,rear = -1;
void insert_queue(int vertex);
int delete_queue();
int isEmpty_queue();
 
int main()
{
	create_graph();
	BF_Traversal();
	return 0;
}
 
void BF_Traversal()
{
	int v;
	
	for(v=0; v<n; v++) 
		state[v] = initial;
	
	printf("Enter Start Vertex for BFS: \n");
	scanf("%d", &v);
	BFS(v);
}
 
void BFS(int v)
{
	int i;
	
	insert_queue(v);
	state[v] = waiting;
	
	while(!isEmpty_queue())
	{
		v = delete_queue( );
		printf("%d ",v);
		state[v] = visited;
		
		for(i=0; i<n; i++)
		{
			if(adj[v][i] == 1 && state[i] == initial) 
			{
				insert_queue(i);
				state[i] = waiting;
			}
		}
	}
	printf("\n");
}
 
void insert_queue(int vertex)
{
	if(rear == MAX-1)
		printf("Queue Overflow\n");
	else
	{
		if(front == -1) 
			front = 0;
		rear = rear+1;
		queue[rear] = vertex ;
	}
}
 
int isEmpty_queue()
{
	if(front == -1 || front > rear)
		return 1;
	else
		return 0;
}
 
int delete_queue()
{
	int delete_item;
	if(front == -1 || front > rear)
	{
		printf("Queue Underflow\n");
		exit(1);
	}
	
	delete_item = queue[front];
	front = front+1;
	return delete_item;
}
 
void create_graph()
{
	int count,max_edge,origin,destin;
 
	printf("Enter number of vertices : ");
	scanf("%d",&n);
	max_edge = n*(n-1);
 
	for(count=1; count<=max_edge; count++)
	{
		printf("Enter edge %d( -1 -1 to quit ) : ",count);
		scanf("%d %d",&origin,&destin);
 
		if((origin == -1) && (destin == -1))
			break;
 
		if(origin>=n || destin>=n || origin<0 || destin<0)
		{
			printf("Invalid edge!\n");
			count--;
		}
		else
		{
			adj[origin][destin] = 1;
		}
	}
}