我尝试使用python和pygame实现最短路径查找算法。算法和可视化似乎有效。然而，当我将开始节点和结束节点彼此远离时，找到路径所需的时间呈指数级增长。找到一条长度为5或6个节点的路径需要数小时。我认为问题出在astar函数中的一个循环上，但我不知道是哪一个以及如何解决。我在互联网上搜索了这个问题，但找不到任何解决方案。这是代码：
import pygame
class cube():
rows = 30
w = 840
def __init__(self, pos=None, color=None):
self.pos = pos
self.color = color
self.neighbours = []
def draw(self, surface):
dis = self.w // self.rows
i = self.pos[0]
j = self.pos[1]
pygame.draw.rect(surface, self.color, (i * dis + 1, j * dis + 1, dis - 2, dis - 2))
class node(cube):
def __init__(self, pos=None, color=None, parent=None):
super().__init__(pos, color)
self.parent = parent
self.g = 0
self.h = 0
self.f = self.g + self.h
def __eq__(self, other):
return self.pos == other.pos
//here is the astar function
def astar(start, end):
global rows, path, obs_list, start_node, end_node, window, closed_list, blue, children, red, green, grey
counter = 0
green = (0,255,0)
red = (255,0,0)
blue = (0,0,255)
grey = (170,170,170)
start_node = node(start, red)
end_node = node(end, red)
start_node.g = start_node.h = start_node.f = 0
end_node.g = end_node.h = end_node.f = 0
open_list = []
closed_list = []
open_list.append(start_node)
while len(open_list) > 0:
# Get the current node
current_node = open_list[0]
current_index = 0
for index, item in enumerate(open_list):
if item.f < current_node.f:
current_node = item
current_index = index
# Pop current off open list, add to closed list
open_list.pop(current_index)
closed_list.append(current_node)
visualize(window, open_list)
if current_node.pos == end_node.pos:
path = []
current = current_node
while current is not None:
path.append(current.pos)
current = current.parent
return path[::-1] # Return reversed path
children = []
for new_position in [(0, -1), (0, 1), (-1, 0), (1, 0), (-1, -1), (-1, 1), (1, -1), (1, 1)]:
node_position = (current_node.pos[0] + new_position[0], current_node.pos[1] + new_position[1])
#check if neighbour isn't a obstacle
if node_position in obs_list:
# print("not possible")
continue
#check if neighbour isn't in closed list
#create a new node
new_node = node(node_position, green, current_node)
# new node is the child of the previous node. Add child node to the list
children.append(new_node)
# print(children)
#loop through children
for child in children:
for closed_child in closed_list:
if child == closed_child:
continue
child.g = current_node.g + 10
child.h = ((child.pos[0] - end_node.pos[0]) **2) + ((child.pos[1] - end_node.pos[1]) **2)
child.f = child.g + child.h
for open_node in open_list:
if child == open_node and child.g > open_node.g:
continue
# visualize(window, children)
# Add the child to the open list
open_list.append(child)
def draw_grid(w, rows, window):
size_between = w // rows
x = 0
y = 0
for l in range(rows):
x = x + size_between
y = y + size_between
pygame.draw.line(window, (255,255,255), (x, 0), (x, w))
pygame.draw.line(window, (255,255,255), (0,y), (w,y))
def visualize(surface, list):
global red, blue, green, grey, counter
for i,c in enumerate(list):
c.draw(surface)
pygame.display.update()
def show_path(surface):
global path
for i in path:
node_path = cube(i, color=(0,0,255))
node_path.draw(surface)
pygame.display.update()
for c in (path):
node_p = cube(c, color=(35, 180, 89))
node_p.draw(surface)
def draw_inital(surface):
surface.fill((0, 0, 0))
draw_grid(840, 30, surface)
start_node.draw(surface)
end_node.draw(surface)
pygame.display.update()
def mouse_press(x):
global rows, window, obs, start_node, end_node, obs_list
t = x[0]
w = x[1]
g1 = t // (840 // rows)
g2 = w // (840 // rows)
obs = cube((g1,g2), (125, 125, 125))
if obs.pos == start_node.pos:
obs.color = (255,0,0)
obs.draw(window)
pygame.display.update()
elif obs.pos == end_node.pos:
obs.color = (255, 0, 0)
obs.draw(window)
pygame.display.update()
else:
if obs.pos not in obs_list:
obs_list.append(obs.pos)
obs.draw(window)
pygame.display.update()
def main():
global start_node, end_node, rows, window, counter, obs_list, start, end
width = 840
rows = 30
window = pygame.display.set_mode((width,width))
start = (12, 24)
end = (12, 26)
obs_list = []
start_node = node(start, color=(255,0,0))
end_node = node(end, color=(255,0,0))
start_node.draw(window)
end_node.draw(window)
draw_inital(window)
loop = True
while loop:
ev = pygame.event.get()
for event in ev:
if event.type == pygame.QUIT:
pygame.quit()
if pygame.mouse.get_pressed()[0]:
try:
pos = pygame.mouse.get_pos()
mouse_press(pos)
except AttributeError:
pass
elif event.type == pygame.KEYDOWN:
if event.key == pygame.K_SPACE:
loop = False
break
path = astar(start, end)
print(path)
show_path(window)
running = True
while running:
for event in pygame.event.get():
if event.type == pygame.QUIT:
running = False
main()
您的代码很难阅读。以下是一些观察结果。
小错误
child.g = current_node.g + 10
需要成为
child.g = current_node.g + 1
这解决了问题，但只能靠运气。这实际上不是解决方案
真正的Bug
您在open_list中添加了太多元素。
for new_position in ...:
# create a new node
new_node = node(node_position, green, current_node)
...
children.append(new_node)
# print(children)
# loop through children
for child in children:
...
open_list.append(child)
请注意，对于每个邻居(for new_position in ...((8x(，您将附加一个将新的child添加到children列表中，然后对迄今为止的所有children进行迭代。这是1/2 * 8 * 8 = 32儿童添加的。
一个简单的解决方案是每个邻居/子节点只有一个循环，而不是您当前拥有的两个循环
优先级队列
您没有将优先级队列用于打开的列表。这意味着，对于从打开的列表中弹出的每个元素，都要扫描整个列表。
使用此：https://docs.python.org/3/library/heapq.html
设置成员身份
for closed_child in closed_list:
if child == closed_child:
continue
应该变成，但需要使"节点"类型可散列：
closed_list = set()
...
if child in closed_list:
continue
启发式函数
错误：你在计算欧几里得距离时忘记了平方根。