scientific-programming-exercises/exam/ex01/graph.py

from collections import deque, defaultdict
import logging

from cfg import config
import sql

logger = logging.getLogger(__name__)


class DijkstraHelper(object):
	def __init__(self, nodes, connections):
		self._nodes = {node: float("inf") for node in nodes}
		self._connections = connections
		self._todo_in_next_step = set()

	@classmethod
	def from_db(cls, connection):
		cursor = connection.cursor()
		cursor.execute(sql.statements["get_all_page_ids"])
		nodes = [n[0] for n in cursor.fetchall()]
		connections = defaultdict(list)

		cursor.execute(sql.statements["get_links"])
		for source, destination in cursor:
			connections[source].append(destination)

		return cls(nodes, connections)

	def dijkstra(self, root):
		self.recursive_dijkstra([root], 0)

	def recursive_dijkstra(self, todos, depth):
		if(not todos):
			return
		logger.info("recursive_dijkstra(<{} nodes>, {})".format(len(todos), depth))
		next_todos = deque()
		for todo in todos:
			next_todos.extend(self.dijkstra_one(todo, depth))

		self.recursive_dijkstra(next_todos, depth + 1)

	def dijkstra_one(self, node, depth):
		for neighbor in self._connections[node]:
			if(self._nodes[neighbor] <= depth):
				continue
			self._nodes[neighbor] = depth
			yield neighbor

	def write_back(self, connection):
		cursor = connection.cursor()
		cursor.execute(sql.statements["delete_dijkstra"])
		cursor.executemany(sql.statements["insert_dijkstra_values"], list(self._nodes.items()))