-
Notifications
You must be signed in to change notification settings - Fork 1
/
astar.py
98 lines (73 loc) · 2.87 KB
/
astar.py
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
import heapq
class SquareGrid:
def __init__(self, width, height):
self.width = width
self.height = height
self.walls = []
def in_bounds(self, id):
(x, y) = id
return 0 <= x < self.width and 0 <= y < self.height
def passable(self, id):
return id not in self.walls
def neighbors(self, id):
(x, y) = id
results = [(x + 1, y), (x, y - 1), (x - 1, y), (x, y + 1)]
if (x + y) % 2 == 0: results.reverse() # aesthetics
results = filter(self.in_bounds, results)
results = filter(self.passable, results)
return results
class GridWithWeights(SquareGrid):
def __init__(self, width, height):
super().__init__(width, height)
self.weights = {}
def cost(self, from_node, to_node):
return self.weights.get(to_node, 1)
diagram4 = GridWithWeights(10, 10)
diagram4.walls = [(1, 7), (1, 8), (2, 7), (2, 8), (3, 7), (3, 8)]
diagram4.weights = {loc: 5 for loc in [(3, 4), (3, 5), (4, 1), (4, 2),
(4, 3), (4, 4), (4, 5), (4, 6),
(4, 7), (4, 8), (5, 1), (5, 2),
(5, 3), (5, 4), (5, 5), (5, 6),
(5, 7), (5, 8), (6, 2), (6, 3),
(6, 4), (6, 5), (6, 6), (6, 7),
(7, 3), (7, 4), (7, 5)]}
class PriorityQueue:
def __init__(self):
self.elements = []
def empty(self):
return len(self.elements) == 0
def put(self, item, priority):
heapq.heappush(self.elements, (priority, item))
def get(self):
return heapq.heappop(self.elements)[1]
def heuristic(a, b):
(x1, y1) = a
(x2, y2) = b
return abs(x1 - x2) + abs(y1 - y2)
def a_star_search(graph, start, goal):
frontier = PriorityQueue()
frontier.put(start, 0)
came_from = {}
cost_so_far = {}
came_from[start] = None
cost_so_far[start] = 0
while not frontier.empty():
current = frontier.get()
if current == goal:
break
for next in graph.neighbors(current):
new_cost = cost_so_far[current] + graph.cost(current, next)
if next not in cost_so_far or new_cost < cost_so_far[next]:
cost_so_far[next] = new_cost
priority = new_cost + heuristic(goal, next)
frontier.put(next, priority)
came_from[next] = current
return came_from, cost_so_far
from implementation import *
start, goal = (1, 4), (7, 8)
came_from, cost_so_far = a_star_search(diagram4, start, goal)
draw_grid(diagram4, width=3, point_to=came_from, start=start, goal=goal)
print()
draw_grid(diagram4, width=3, number=cost_so_far, start=start, goal=goal)
print()
draw_grid(diagram4, width=3, path=reconstruct_path(came_from, start=(1, 4), goal=(7, 8)))