A*（A星）算法python实现
在春节放假前两天我偶然看到了A\*算法（A\*算法是一个启发式的地图寻路算法），感觉挺有意思。正好放假前也没有什么事情，就花了一个下午写出算法的骨架，节后又花了半天时间完善屏幕输出的细节并且调试完成。
该实现只是一时兴起的随手而作，没有考虑性能和扩展性等问题。正在学习A\*算法的朋友可以拿去随便折腾。
Email: wang.zhigang@hotmail.com
代码的运行效果如下：
```pytho
#!/usr/bin/python
# vim:set fileencoding=utf-8
# 在春节放假前两天我偶然看到了A*算法，感觉挺有意思。正好放假前
# 也没有什么事情，就花了一个下午写出算法的骨架，节后又花了半天
# 时间完善屏幕输出的细节并且调试完成。
# 该实现只是一时兴起的随手而作，没有考虑性能和扩展性等问题。正
# 在学习A*的朋友可以拿去随便折腾。
# email: wang.zhigang@hotmail.com
import sys
_2dmap = []
start = None
end = None
open_list = {}
close_list = {}
map_border = ()
class Node:
def __init__(this, father, x, y):
if x < 0 or x >= map_border[0] or y < 0 or y >= map_border[1]:
raise Exception("node position can't beyond the border!")
this.father = father
this.x = x
this.y = y
if father != None:
G2father = calc_G(father, this)
if not G2father:
raise Exception("father is not valid!")
this.G = G2father + father.G
this.H = calc_H(this, end)
this.F = this.G + this.H
else:
this.G = 0
this.H = 0
this.F = 0
def reset_father(this, father, new_G):
if father != None:
this.G = new_G
this.F = this.G + this.H
this.father = father
def calc_G(node1, node2):
x1 = abs(node1.x-node2.x)
y1 = abs(node1.y-node2.y)
if (x1== 1 and y1 == 0):
return 10 # same row
if (x1== 0 and y1 == 1):
return 10 # same col
if (x1== 1 and y1 == 1):
return 14 # cross
else:
return 0
def calc_H(cur, end):
return abs(end.x-cur.x) + abs(end.y-cur.y)
# NOTE 这个地方可能成为性能瓶颈
def min_F_node():
if len(open_list) == 0:
raise Exception("not exist path!")
_min = 9999999999999999
_k = (start.x, start.y)
for k,v in open_list.items():
if _min > v.F:
_min = v.F
_k = k
return open_list[_k]
# 把相邻节点加入open list, 如果发现终点说明找到了路径
def addAdjacentIntoOpen(node):
# 将该节点从开放列表移到关闭列表当中。
open_list.pop((node.x, node.y))
close_list[(node.x, node.y)] = node
_adjacent = []
# 相邻节点还没有注意边界的情况
try:
_adjacent.append(Node(node , node.x - 1 , node.y - 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x , node.y - 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x + 1 , node.y - 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x + 1 , node.y))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x + 1 , node.y + 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x , node.y + 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x - 1 , node.y + 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x - 1 , node.y))
except Exception,e:
pass
for a in _adjacent:
if (a.x,a.y) == (end.x, end.y):
new_G = calc_G(a, node) + node.G
end.reset_father(node, new_G)
print "find path finish!"
return True
if (a.x,a.y) in close_list:
continue
if (a.x,a.y) not in open_list:
open_list[(a.x,a.y)] = a
else:
exist_node = open_list[(a.x,a.y)]
new_G = calc_G(a, node) + node.G
if new_G < exist_node.G:
exist_node.reset_father(node, new_G)
return False
def find_the_path(start, end):
open_list[(start.x, start.y)] = start
the_node = start
try:
while not addAdjacentIntoOpen(the_node):
the_node = min_F_node()
except Exception,e:
# path not exist
print e
return False
return True
#=======================================================================
def print_map():
print ' Y',
for i in xrange(len(_2dmap)):
print i,
print
print ' X'
row = 0
for l in _2dmap:
print '%3d'%row,' ',
row = row+1
for i in l:
print i,
print
def mark_path(node):
if node.father == None:
return
_2dmap[node.x][node.y] = '#'
mark_path(node.father)
def preset_map():
global start,end,map_border
_2dmap.append('S X . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. X . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. X . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . . . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X X X X .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X X X'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . E'.split())
map_border = (len(_2dmap),len(_2dmap[0]))
row_index = 0
for row in _2dmap:
col_index = 0
for n in row:
if n == 'X':
block_node = Node(None, row_index, col_index)
close_list[(block_node.x, block_node.y)] = block_node
elif n == 'S':
start = Node(None, row_index, col_index)
elif n == 'E':
end = Node(None, row_index, col_index)
col_index = col_index + 1
row_index = row_index + 1
if __name__=='__main__':
if len(sys.argv) < 3:
preset_map()
else:
x = int(sys.argv[1])
y = int(sys.argv[2])
map_border = (x,y)
_start = raw_input('pls input start point:')
_end = raw_input('pls input end point:')
_start = _start.split(',')
_end = _end.split(',')
_start = (int(_start[0]), int(_start[1]))
_end = (int(_end[0]), int(_end[1]))
start = Node(None, _start[0], _start[1])
end = Node(None, _end[0], _end[1])
# gen map
_2dmap = [['.' for i in xrange(y)] for i in xrange(x) ]
# put start and end
_2dmap[_start[0]][_start[1]] = 'S'
_2dmap[_end[0]][_end[1]] = 'E'
# input blocks
while True:
_block = raw_input('input block:')
if not _block:
break
_block = _block.split(',')
_block = (int(_block[0]), int(_block[1]))
_2dmap[_block[0]][_block[1]] = 'X'
block_node = Node(None, _block[0], _block[1])
close_list[(block_node.x, block_node.y)] = block_node
print "orignal map:"
print_map()
if find_the_path(start, end):
mark_path(end.father)
print "found road as follow:"
print_map()
```
该实现只是一时兴起的随手而作，没有考虑性能和扩展性等问题。正在学习A\*算法的朋友可以拿去随便折腾。
Email: wang.zhigang@hotmail.com
代码的运行效果如下：
```pytho
#!/usr/bin/python
# vim:set fileencoding=utf-8
# 在春节放假前两天我偶然看到了A*算法，感觉挺有意思。正好放假前
# 也没有什么事情，就花了一个下午写出算法的骨架，节后又花了半天
# 时间完善屏幕输出的细节并且调试完成。
# 该实现只是一时兴起的随手而作，没有考虑性能和扩展性等问题。正
# 在学习A*的朋友可以拿去随便折腾。
# email: wang.zhigang@hotmail.com
import sys
_2dmap = []
start = None
end = None
open_list = {}
close_list = {}
map_border = ()
class Node:
def __init__(this, father, x, y):
if x < 0 or x >= map_border[0] or y < 0 or y >= map_border[1]:
raise Exception("node position can't beyond the border!")
this.father = father
this.x = x
this.y = y
if father != None:
G2father = calc_G(father, this)
if not G2father:
raise Exception("father is not valid!")
this.G = G2father + father.G
this.H = calc_H(this, end)
this.F = this.G + this.H
else:
this.G = 0
this.H = 0
this.F = 0
def reset_father(this, father, new_G):
if father != None:
this.G = new_G
this.F = this.G + this.H
this.father = father
def calc_G(node1, node2):
x1 = abs(node1.x-node2.x)
y1 = abs(node1.y-node2.y)
if (x1== 1 and y1 == 0):
return 10 # same row
if (x1== 0 and y1 == 1):
return 10 # same col
if (x1== 1 and y1 == 1):
return 14 # cross
else:
return 0
def calc_H(cur, end):
return abs(end.x-cur.x) + abs(end.y-cur.y)
# NOTE 这个地方可能成为性能瓶颈
def min_F_node():
if len(open_list) == 0:
raise Exception("not exist path!")
_min = 9999999999999999
_k = (start.x, start.y)
for k,v in open_list.items():
if _min > v.F:
_min = v.F
_k = k
return open_list[_k]
# 把相邻节点加入open list, 如果发现终点说明找到了路径
def addAdjacentIntoOpen(node):
# 将该节点从开放列表移到关闭列表当中。
open_list.pop((node.x, node.y))
close_list[(node.x, node.y)] = node
_adjacent = []
# 相邻节点还没有注意边界的情况
try:
_adjacent.append(Node(node , node.x - 1 , node.y - 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x , node.y - 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x + 1 , node.y - 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x + 1 , node.y))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x + 1 , node.y + 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x , node.y + 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x - 1 , node.y + 1))
except Exception,e:
pass
try:
_adjacent.append(Node(node , node.x - 1 , node.y))
except Exception,e:
pass
for a in _adjacent:
if (a.x,a.y) == (end.x, end.y):
new_G = calc_G(a, node) + node.G
end.reset_father(node, new_G)
print "find path finish!"
return True
if (a.x,a.y) in close_list:
continue
if (a.x,a.y) not in open_list:
open_list[(a.x,a.y)] = a
else:
exist_node = open_list[(a.x,a.y)]
new_G = calc_G(a, node) + node.G
if new_G < exist_node.G:
exist_node.reset_father(node, new_G)
return False
def find_the_path(start, end):
open_list[(start.x, start.y)] = start
the_node = start
try:
while not addAdjacentIntoOpen(the_node):
the_node = min_F_node()
except Exception,e:
# path not exist
print e
return False
return True
#=======================================================================
def print_map():
print ' Y',
for i in xrange(len(_2dmap)):
print i,
print ' X'
row = 0
for l in _2dmap:
print '%3d'%row,' ',
row = row+1
for i in l:
print i,
def mark_path(node):
if node.father == None:
return
_2dmap[node.x][node.y] = '#'
mark_path(node.father)
def preset_map():
global start,end,map_border
_2dmap.append('S X . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. X . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. X . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . . . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X X X X .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X X X'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . . . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . .'.split())
_2dmap.append('. . . . . . . . . . . . . . . X . X . E'.split())
map_border = (len(_2dmap),len(_2dmap[0]))
row_index = 0
for row in _2dmap:
col_index = 0
for n in row:
if n == 'X':
block_node = Node(None, row_index, col_index)
close_list[(block_node.x, block_node.y)] = block_node
elif n == 'S':
start = Node(None, row_index, col_index)
elif n == 'E':
end = Node(None, row_index, col_index)
col_index = col_index + 1
row_index = row_index + 1
if __name__=='__main__':
if len(sys.argv) < 3:
preset_map()
else:
x = int(sys.argv[1])
y = int(sys.argv[2])
map_border = (x,y)
_start = raw_input('pls input start point:')
_end = raw_input('pls input end point:')
_start = _start.split(',')
_end = _end.split(',')
_start = (int(_start[0]), int(_start[1]))
_end = (int(_end[0]), int(_end[1]))
start = Node(None, _start[0], _start[1])
end = Node(None, _end[0], _end[1])
# gen map
_2dmap = [['.' for i in xrange(y)] for i in xrange(x) ]
# put start and end
_2dmap[_start[0]][_start[1]] = 'S'
_2dmap[_end[0]][_end[1]] = 'E'
# input blocks
while True:
_block = raw_input('input block:')
if not _block:
break
_block = _block.split(',')
_block = (int(_block[0]), int(_block[1]))
_2dmap[_block[0]][_block[1]] = 'X'
block_node = Node(None, _block[0], _block[1])
close_list[(block_node.x, block_node.y)] = block_node
print "orignal map:"
print_map()
if find_the_path(start, end):
mark_path(end.father)
print "found road as follow:"
print_map()
```
