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

from collections import deque

from cfg import config

def prepare_dijkstra(connection):
	cursor = connection.cursor()
	cursor.execute('''INSERT OR IGNORE INTO dijkstra_helper(name) 
			SELECT destination FROM links
			''')
		
	if(config["use_sqlite"]):
		cursor.execute("UPDATE dijkstra_helper SET value=1e1000")
	else:
		cursor.execute("UPDATE dijkstra_helper SET value=2147483647")
	connection.commit()

def dijkstra_one(title, value, connection):
	cursor = connection.cursor()
	if(isinstance(title, tuple)):
		# Idk why this happens.
		title = title[0]
	cursor.execute('''SELECT name 
			FROM dijkstra_helper 
			LEFT JOIN links ON links.destination=dijkstra_helper.name
			WHERE links.source=:title 
				AND dijkstra_helper.value>:value''', {"title": title, "value": value + 1})
	# This is the list of nodes that have to be updated
	result = cursor.fetchall()

	cursor.execute('''UPDATE dijkstra_helper 
			SET value=:value
			WHERE name IN (
				SELECT destination
				FROM links 
				WHERE source=:title)
			AND dijkstra_helper.value>:value''', {"value": value + 1, "title": title})
	connection.commit()
	return result

def recursive_dijkstra(titles, value, connection):
	if(not titles):
		return

	todos = deque()
	for title in titles:
		todos.extend(dijkstra_one(title, value, connection))

	recursive_dijkstra(todos, value + 1, connection)


def dijkstra(title, connection):
	cursor = connection.cursor()
	cursor.execute("UPDATE dijkstra_helper SET value=0 WHERE name=%s", (title,))

	todos = dijkstra_one(title, 1, connection)
	recursive_dijkstra(todos, 2, connection)