Created
March 9, 2018 05:20
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Pseudo code for an A* path solver
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#!/usr/bin/python | |
import heapq | |
class Cell(object): | |
def __init__(self, x, y, is_wall): | |
self.reachable = not is_wall | |
self.x = x | |
self.y = y | |
self.parent = None | |
# G, H, F are current costs | |
self.g = 0 # cost to get to end pos | |
self.h = 0 # cost to get to from start pos | |
self.f = 0 # g + h | |
class AStar(object): | |
def __init__(self, maze): | |
# Open cells to still visit | |
self.opened = [] | |
heapq.heapify(self.opened) | |
# Visited cells list | |
self.closed = set() | |
# Initialize all cells | |
self.init_grid() | |
def init_grid(self): | |
# Create cells by looping through the input maze | |
for x in range(self.grid_width): | |
for y in range(self.grid_height): | |
if self.maze[y][x] == 1: | |
is_wall = True | |
else: | |
is_wall = False | |
self.cells.append(Cell(x, y, is_wall)) | |
def solve(self): | |
# Add starting cell to open heap queue | |
heapq.heappush(self.opened, (self.start.f, self.start)) | |
while len(self.opened): | |
# Pop cell from heap queue | |
f, cell = heapq.heappop(self.opened) | |
# Add cell to closed list so we don't process it twice | |
self.closed.add(cell) | |
# If ending cell, return found path | |
if cell is self.end: | |
return self.get_path() | |
# Get adjacent cells for the current cell | |
adj_cells = self.get_adjacent_cells(cell) | |
for adj_cell in adj_cells: | |
# If the adj_cell is not a wall and hasn't been visited | |
if adj_cell.reachable and adj_cell not in self.closed: | |
# If adj_cell in open list from another cell, check if current path is | |
# better than the one previously found for this cell | |
if (adj_cell.f, adj_cell) in self.opened: | |
if adj_cell.g > cell.g + 10: | |
# If so, update its cost and parent with the current cell | |
self.update_cell(adj_cell, cell) | |
else: | |
# If adj_cell has never been visited before, update it with its | |
# cost and parent cell. Add to heap for use | |
self.update_cell(adj_cell, cell) | |
heapq.heappush(self.opened, (adj_cell.f, adj_cell)) | |
def answer(maze): | |
astar = AStar(maze) | |
return astar.solve() | |
maze = [[0, 0, 0, 0, 0, 0], | |
[1, 1, 1, 1, 1, 0], | |
[0, 0, 0, 0, 0, 0], | |
[0, 1, 1, 1, 1, 1], | |
[0, 1, 1, 1, 1, 1], | |
[0, 0, 0, 0, 0, 0]] | |
print answer(maze) |
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