python实现AI版贪吃蛇

一、主要思路

（1）蛇每走一步，就使用BFS计算游戏界面中每个位置（蛇身除外）到达食物的最短路径长；

（2）将蛇的安全定义为蛇是否可以跟着蛇尾运动，即蛇头和蛇尾间是否存在路径；

（3）蛇每次行动前先利用虚拟的蛇进行探路，若虚拟的蛇吃完食物后是安全的，真蛇才行动；

（4）若蛇和食物之间不存在路径或者吃完食物后并不安全，就跟着蛇尾走；

（5）若蛇和食物之间、蛇和蛇尾之间均不存在路径，就随便挑一步可行的来走；

（6）保证目标是食物时蛇走最短路径，目标是蛇尾时蛇走最长路径。

二、实现代码

部分功能代码如下：

画网格

def drawGrid():
 # 垂直方向
 for x in range(0, SCREENWIDTH, CELLSIZE):
  pygame.draw.line(screen, (40, 40, 40), (x, 0), (x, SCREENHEIGHT))
 # 水平方向
 for y in range(0, SCREENHEIGHT, CELLSIZE):
  pygame.draw.line(screen, (40, 40, 40), (0, y), (SCREENWIDTH, y))

显示蛇

def ShowSnake(coords):
 x = coords[0]['x'] * CELLSIZE
 y = coords[0]['y'] * CELLSIZE
 head_rect = pygame.Rect(x, y, CELLSIZE, CELLSIZE)
 pygame.draw.rect(screen, (0, 80, 255), head_rect)
 head_inner_rect = pygame.Rect(x + 4, y + 4, CELLSIZE - 8, CELLSIZE - 8)
 pygame.draw.rect(screen, (0, 80, 255), head_inner_rect)
 for coord in coords[1:]:
  x = coord['x'] * CELLSIZE
  y = coord['y'] * CELLSIZE
  rect = pygame.Rect(x, y, CELLSIZE, CELLSIZE)
  pygame.draw.rect(screen, (0, 155, 0), rect)
  inner_rect = pygame.Rect(x + 4, y + 4, CELLSIZE - 8, CELLSIZE - 8)
  pygame.draw.rect(screen, (0, 255, 0), inner_rect)

显示果实

def ShowApple(coord):
 x = coord['x'] * CELLSIZE
 y = coord['y'] * CELLSIZE
 rect = pygame.Rect(x, y, CELLSIZE, CELLSIZE)
 pygame.draw.rect(screen, (255, 0, 0), rect)

显示当前得分

def ShowScore(score):
 score_render = default_font.render('得分: %s' % (score), True, (255, 255, 255))
 rect = score_render.get_rect()
 rect.topleft = (SCREENWIDTH-120, 10)
 screen.blit(score_render, rect)

显示结束界面

def ShowEndInterface():
 title_font = pygame.font.Font('simkai.ttf', 100)
 title_game = title_font.render('Game', True, (233, 150, 122))
 title_over = title_font.render('Over', True, (233, 150, 122))
 game_rect = title_game.get_rect()
 over_rect = title_over.get_rect()
 game_rect.midtop = (SCREENWIDTH/2, 70)
 over_rect.midtop = (SCREENWIDTH/2, game_rect.height+70+25)
 screen.blit(title_game, game_rect)
 screen.blit(title_over, over_rect)
 pygame.display.update()
 pygame.time.wait(500)
 while True:
  for event in pygame.event.get():
   if event.type == pygame.QUIT or (event.type == pygame.KEYDOWN and event.key == pygame.K_ESCAPE):
    CloseGame()

广度优先遍历, 计算每个非SNAKENUM元素到达食物的路径长度

def RefreshBoard(psnake, pfood, pboard):
 temp_board = pboard[:]
 pfood_idx = pfood['x'] + pfood['y'] * MATRIX_W
 queue = []
 queue.append(pfood_idx)
 inqueue = [0] * MATRIX_SIZE
 found = False
 while len(queue) != 0:
  idx = queue.pop(0)
  if inqueue[idx] == 1:
   continue
  inqueue[idx] = 1
  for move_direction in ['left', 'right', 'up', 'down']:
   if isMovePossible(idx, move_direction):
    if (idx + MOVEDIRECTIONS[move_direction]) == (psnake[HEADINDEX]['x'] + psnake[HEADINDEX]['y'] * MATRIX_W):
     found = True
    # 该点不是蛇身(食物是0才可以这样子写)
    if temp_board[idx + MOVEDIRECTIONS[move_direction]] < SNAKENUM:
     if temp_board[idx + MOVEDIRECTIONS[move_direction]] > temp_board[idx]+1:
      temp_board[idx + MOVEDIRECTIONS[move_direction]] = temp_board[idx] + 1
     if inqueue[idx + MOVEDIRECTIONS[move_direction]] == 0:
      queue.append(idx + MOVEDIRECTIONS[move_direction])

三、效果展示

四、不足之处

  由于食物是随机出现的，若虚拟的蛇跑一遍发现去吃食物是不安全的，真蛇就不会去吃食物，而是选择追着蛇尾跑，若一直如此，就陷入了死循环，蛇一直追着蛇尾跑，直到你终止游戏为止。