https://en.wikipedia.org/wiki/Bidirectional_search
>>> astar = AStar((0, 0), (len(grid) - 1, len(grid[0]) - 1))
>>> (astar.start.pos_y + delta[3][0], astar.start.pos_x + delta[3][1])
(0, 1)
>>> [x.pos for x in astar.get_successors(astar.start)]
[(1, 0), (0, 1)]
>>> (astar.start.pos_y + delta[2][0], astar.start.pos_x + delta[2][1])
(1, 0)
>>> astar.retrace_path(astar.start)
[(0, 0)]
>>> astar.search()
[(0, 0), (1, 0), (2, 0), (2, 1), (2, 2), (2, 3), (3, 3),
(4, 3), (4, 4), (5, 4), (5, 5), (6, 5), (6, 6)]
Returns a list of successors (both in the grid and free spaces)
Retrace the path from parents to parents until start node
>>> bd_astar = BidirectionalAStar((0, 0), (len(grid) - 1, len(grid[0]) - 1))
>>> bd_astar.fwd_astar.start.pos == bd_astar.bwd_astar.target.pos
True
>>> bd_astar.retrace_bidirectional_path(bd_astar.fwd_astar.start,
... bd_astar.bwd_astar.start)
[(0, 0)]
>>> bd_astar.search()
[(0, 0), (0, 1), (0, 2), (1, 2), (1, 3), (2, 3), (2, 4),
(2, 5), (3, 5), (4, 5), (5, 5), (5, 6), (6, 6)]
>>> k = Node(0, 0, 4, 3, 0, None)
>>> k.calculate_heuristic()
5.0
>>> n = Node(1, 4, 3, 4, 2, None)
>>> n.calculate_heuristic()
2.0
>>> l = [k, n]
>>> n == l[0]
False
>>> l.sort()
>>> n == l[0]
True
Heuristic for the A*