解决迷宫的 BFS 算法不起作用，多次检查相同的数字

Question

我正在尝试创建一个迷宫解决算法。我在网上看了一些教程，并遇到了 BFS 算法。我试着自己实现它。这是我写的：

import queue, numpy, time
from PIL import Image

def maze(mazename, start=True, end=True):
    q = queue.Queue()
    img = Image.open(mazename)
    array = numpy.array(img).tolist()
    for x, y in enumerate(array):
        for i, h in enumerate(y):
            if h == 0:
                array[x][i] = (0, 0, 0)
            else:
                array[x][i] = (255, 255, 255)
    if start and end:
        for x, y in enumerate(array[0]):
            if y == (255, 255, 255):
                start = [x+1, 1]
        for x, y in enumerate(array[-1]):
            if y == (255, 255, 255):
                end = [x+1, len(array)]
    start[0] = start[0]-1
    start[1] = start[1]-1
    end[0] = end[0]-1
    end[1] = end[1]-1
    start = tuple(start)
    q.put("")
    while True:
        #Checking for end
        parse = q.get()
        m = list(start)
        for i in parse:
            if i == "D":
                m[1] = m[1]+1
            if i == "U":
                m[1] = m[1]-1
            if i == "L":
                m[0] = m[0]-1
            if i == "R":
                m[0] = m[0]+1
        print(m, end)
        if m == end:
            m = list(start)
            array[m[1]][m[0]] = (255, 0, 0)
            for i in parse:
                if i == "D":
                    m[1] = m[1]+1
                    array[m[1]][m[0]] = (255, 0, 0)
                if i == "U":
                    m[1] = m[1]-1
                    array[m[1]][m[0]] = (255, 0, 0)
                if i == "L":
                    m[0] = m[0]-1
                    array[m[1]][m[0]] = (255, 0, 0)
                if i == "R":
                    m[0] = m[0]+1
                    array[m[1]][m[0]] = (255, 0, 0)
            return array
        #Find new trails
        directions = ["U", "D", "L", "R"]
        if m[0] == 0:
            directions.remove("L")
        elif array[m[1]][m[0]-1] == (0, 0, 0):
            directions.remove("L")
        if m[0]+1 == len(array[0]):
            directions.remove("R")
        elif array[m[1]][m[0]+1] == (0, 0, 0):
            directions.remove("R")
        if m[1] == 0:
            directions.remove('U')
        elif array[m[1]-1][m[0]] == (0, 0, 0):
            directions.remove('U')
        if m[1]+1 == len(array):
            directions.remove("D")
        elif array[m[1]+1][m[0]] == (0, 0, 0):
            directions.remove("D")
        for direction in directions:
            q.put(parse+direction)

t1 = time.time()
arr = maze(input("Enter maze file name: "))
print(time.time()-t1)
Image.fromarray(numpy.array(arr).astype(numpy.uint8)).show()

我在这张图片上试过了：https://raw.githubusercontent.com/mikepound/mazesolving/master/examples/tiny.png 它工作得很好。花了 3 到 7 秒。

然后我在这张图片上试了一下： https://raw.githubusercontent.com/mikepound/mazesolving/master/examples/normal.png

它已经运行了 15 分钟，但仍然没有通过 40x40 图像的第 10 行一次。它检查相同的数字数百次，我不知道为什么。有人可以指出我算法中的缺陷并帮助我修复它吗？我试过实现一个访问列表，它只会减慢程序的速度。谢谢

Answer 1

您缺少visited 的列表。您应该跟踪到目前为止您去过的地方，以免重复相同的位置。

当你有一个访问过的列表时，你可以在移动之前使用它来检查你是否已经在那个像素处。

   def maze(mazename, start=True, end=True):
    q = queue.Queue()
    visited = []
    img = Image.open(mazename)
    array = numpy.array(img).tolist()
    for x, y in enumerate(array):
        for i, h in enumerate(y):
            if h == 0:
                array[x][i] = (0, 0, 0)
            else:
                array[x][i] = (255, 255, 255)
    if start and end:
        for x, y in enumerate(array[0]):
            if y == (255, 255, 255):
                start = [x+1, 1]
        for x, y in enumerate(array[-1]):
            if y == (255, 255, 255):
                end = [x+1, len(array)]
    start[0] = start[0]-1
    start[1] = start[1]-1
    end[0] = end[0]-1
    end[1] = end[1]-1
    start = tuple(start)
    q.put("")
    while True:
        #Checking for end
        parse = q.get()
        m = list(start)
        for i in parse:
            if i == "D":
                m[1] = m[1]+1
            if i == "U":
                m[1] = m[1]-1
            if i == "L":
                m[0] = m[0]-1
            if i == "R":
                m[0] = m[0]+1
        if m not in visited:
            visited.append(m)
            print(m, end)
            if m == end:
                m = list(start)
                array[m[1]][m[0]] = (255, 0, 0)
                for i in parse:
                    if i == "D":
                        m[1] = m[1]+1
                        array[m[1]][m[0]] = (255, 0, 0)
                    if i == "U":
                        m[1] = m[1]-1
                        array[m[1]][m[0]] = (255, 0, 0)
                    if i == "L":
                        m[0] = m[0]-1
                        array[m[1]][m[0]] = (255, 0, 0)
                    if i == "R":
                        m[0] = m[0]+1
                        array[m[1]][m[0]] = (255, 0, 0)
                return array
            #Find new trails
            directions = ["U", "D", "L", "R"]
            if m[0] == 0:
                directions.remove("L")
            elif array[m[1]][m[0]-1] == (0, 0, 0):
                directions.remove("L")
            if m[0]+1 == len(array[0]):
                directions.remove("R")
            elif array[m[1]][m[0]+1] == (0, 0, 0):
                directions.remove("R")
            if m[1] == 0:
                directions.remove('U')
            elif array[m[1]-1][m[0]] == (0, 0, 0):
                directions.remove('U')
            if m[1]+1 == len(array):
                directions.remove("D")
            elif array[m[1]+1][m[0]] == (0, 0, 0):
                directions.remove("D")
            for direction in directions:
                q.put(parse+direction)