Question

所以我正在尝试创建一个泛洪填充算法，并且我不断收到这个错误。该算法似乎具有无限递归，我无法确定原因。我已经浏览了整个互联网，我无法找到解决方案，因为根据大多数消息来源，我的程序似乎是正确的。然而，似乎有些不对劲。这是代码的编辑版本。错误消息仍然是最大递归。

我可以得到一些帮助吗？

    from Tkinter import *
    from PIL import Image, ImageTk
    from random import *


    w= 75
    h= w

    flood = Image.new("RGB", (w,h), (0,0,0))

    x = 0
    y = 0
    count = 0

    colorlist = []
    i = 0

    while x < w -1:
        y = 0
        while y < h-1:
            r = random()
            if r < .25:
                flood.putpixel((x,y), (0,0,0))
            else:
                flood.putpixel((x,y), (255,255,255))
            y += 1
        x += 1
    x = 0
    y = 0
    while x < w-1:
        y = 0
        while y < h-1:
            r = random()
            if x == 0 or y == 0 or x == w-1 or y ==h-1:
                flood.putpixel((x,y), (0,0,0))
            y += 1
        x += 1


    def floodfill(x,y, d,e,f, g,h,i, image, count):
            count+=1
            (a,b,c) = image.getpixel((x,y))
            if (a,b,c) == (255,255,255):
                (j,k,l) = image.getpixel((x-1,y))
                (m,n,o) = image.getpixel((x+1, y))
                (p,q,r) = image.getpixel((x,y-1))
                (s,t,u) = image.getpixel((x,y+1))
            if count > 990:
                return
            if (a,b,c) == (255,255,255):
                image.putpixel((x,y), (g,h,i))
                floodfill(x-1, y, d,e,f, g,h,i, image, count)
                floodfill(x+1, y, d,e,f, g,h,i, image, count)
                floodfill(x, y-1, d,e,f, g,h,i, image, count)
                floodfill(x, y+1, d,e,f, g,h,i, image,count)



    floodfill(2,2, 0,0,0,255,0,0,flood, 0)

    flood.save("flood.png")
    print "done"

Answer 1

Python倾向于抛出maximum recursion depth exceeded错误，即使算法无法无限递归并且最终会自行停止。有两种解决方案：增加递归限制，或切换到迭代算法。

您可以使用sys.setrecursionlimit提高递归限制。选择一个高于算法最差情况递归深度的数字。在您的情况下，这将是图像中的像素数length * height。

将算法更改为迭代算法非常简单，因为绘制像素的顺序并不重要，只要您至少获得一次。 set非常适合保存唯一的非有序数据，因此我们可以使用它来存储我们需要绘制的像素。

def floodFill(x,y, d,e,f, g,h,i, image):
    toFill = set()
    toFill.add((x,y))
    while not toFill.empty():
        (x,y) = toFill.pop()
        (a,b,c) == image.getpixel((x,y))
        if not (a,b,c) == (255, 255, 255):
            continue
        image.putpixel((x,y), (g,h,i))
        toFill.add((x-1,y))
        toFill.add((x+1,y))
        toFill.add((x,y-1))
        toFill.add((x,y+1))
    image.save("flood.png")

如果您使用迭代方法，请务必将绑定检查放入其中。否则，它可能会永远运行！或者至少在您的硬盘驱动器被一个巨大的toFill集合填充之前。

Answer 2

为什么不以depth-first方式进行洪水填充而不是递归？递归使用隐式堆栈，所以你没有什么可失去的。

是的，正如评论中指出的那样，你应该检查x和y是否超出范围。

Answer 3

这尚未经过测试，但主要基于您提供的代码。它应该工作并提供实现floodfill算法的替代方法。该功能可能更有效。

import PIL
import random
import collections

WHITE = 255, 255, 255
BLACK = 0, 0, 0
RED = 255, 0, 0

def main(width, height):
    flood = PIL.Image.new('RGB', (width, height), BLACK)
    # Create randomly generated walls
    for x in range(width):
        for y in range(height):
            flood.putpixel((x, y), BLACK if random.random() < 0.15 else WHITE)
    # Create borders
    for x in range(width):
        for y in range(height):
            if x in {0, width - 1} or y in {0, height - 1}:
                flood.putpixel((x, y), BLACK)
    floodfill(50, 25, RED, image)
    # Save image
    image.save('flood.png')

def floodfill(x, y, color, image):
    # if starting color is different from desired color
    #     create a queue of pixels that need to be changed
    #     while there are pixels that need their color changed
    #         change the color of the pixel to what is desired
    #         for each pixel surrounding the curren pixel
    #             if the new pixel has the same color as the starting pixel
    #                 record that its color needs to be changed
    source = image.getpixel((x, y))
    if source != color:
        pixels = collections.deque[(x, y)]
        while pixels:
            x, y = place = pixels.popleft()
            image.putpixel(place, color)
            for x_offset in -1, 1:
                x_offset += x
                for y_offset in -1, 1:
                    y_offset += y
                    new_place = x_offset, y_offset
                    if image.getpixel(new_place) == source:
                        pixels.append(new_place)

if __name__ == '__main__':
    main(100, 50)

洪水填充算法Python

3 个答案: