Created
July 15, 2009 11:06
-
-
Save bellbind/147645 to your computer and use it in GitHub Desktop.
[Python][library] A* path search
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| def astar(init, goal, nexts, | |
| distance=lambda path: len(path), | |
| heuristic=lambda pos: 0): | |
| import heapq | |
| queue = [] | |
| init_score = distance([init]) + heuristic(init) | |
| checked = {init: init_score} | |
| heapq.heappush(queue, (init_score, [init])) | |
| while len(queue) > 0: | |
| score, path = heapq.heappop(queue) | |
| last = path[-1] | |
| if last == goal: return path | |
| for pos in nexts(last): | |
| newpath = path + [pos] | |
| pos_score = distance(newpath) + heuristic(pos) | |
| if pos in checked and checked[pos] <= pos_score: continue | |
| checked[pos] = pos_score | |
| heapq.heappush(queue, (pos_score, newpath)) | |
| pass | |
| pass | |
| return None | |
| if __name__ == "__main__": | |
| # from: http://d.hatena.ne.jp/pashango_p/20090713/1247455609 | |
| dungeon = [ | |
| 'OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO', | |
| 'OS O O O O O', | |
| 'O O O O O O O OOOO GO', | |
| 'O O O O OOOO O O OOOO', | |
| 'OO OOOOOOOOOOOOOOO O O O O', | |
| 'O O O O O', | |
| 'O OOO O O OOOOOOOOO O', | |
| 'O OO O OOOO O O OO O', | |
| 'O O O O O O O O', | |
| 'O OOO O O O O O', | |
| 'O O O O O', | |
| 'OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO', | |
| ] | |
| def find_ch(ch): | |
| for i, l in enumerate(dungeon): | |
| for j, c in enumerate(l): | |
| if c == ch: return (i, j) | |
| pass | |
| pass | |
| return None | |
| init = find_ch("S") | |
| goal = find_ch("G") | |
| def nexts(pos): | |
| wall = "O" | |
| if dungeon[pos[0] - 1][pos[1]] != wall: yield (pos[0] - 1, pos[1]) | |
| if dungeon[pos[0] + 1][pos[1]] != wall: yield (pos[0] + 1, pos[1]) | |
| if dungeon[pos[0]][pos[1] - 1] != wall: yield (pos[0], pos[1] - 1) | |
| if dungeon[pos[0]][pos[1] + 1] != wall: yield (pos[0], pos[1] + 1) | |
| pass | |
| def heuristic(pos): | |
| return ((pos[0] - goal[0]) ** 2 + (pos[1] - goal[1]) ** 2) ** 0.5 | |
| def distance(path): | |
| return len(path) | |
| def render_path(path): | |
| buf = [[ch for ch in l] for l in dungeon] | |
| for pos in path[1:-1]: buf[pos[0]][pos[1]] = "*" | |
| buf[path[0][0]][path[0][1]] = "s" | |
| buf[path[-1][0]][path[-1][1]] = "g" | |
| return ["".join(l) for l in buf] | |
| path = astar(init, goal, nexts, distance, heuristic) | |
| #path = astar(init, goal, nexts) | |
| print "\n".join(render_path(path)) | |
| pass |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment