def bfs(self, root, display = None, component = None):
        '''
        API: bfs(self, root, display = None, component=None)
        Description:
        Make a breadth-first search starting from node with name root.
        Input:
            root: Starting node name.
            display: display method.
            component: component number.
        Post:
            Nodes will have 'component' attribute that will have component
            number as value.
        '''
        self.search(root, display = display, component = component, q = Queue())