< SNAKE: # 如果该点不是蛇的身体if pboard[idx mov[i]] > pboard[idx] 1:#小于的时候不管，不然会覆盖已有的路径数据 。pboard[idx mov[i]] = pboard[idx]1if inqueue[idx mov[i]] == 0:queue.append(idx mov[i])return found从蛇头开始，根据board中元素值，从蛇头周围4个领域点中选择最短路径 。
def choose_shortest_safe_move(psnake, pboard):best_move = ERRmin = SNAKEfor i in range(4):if is_move_possible(psnake[HEAD], mov[i]) and pboard[psnake[HEAD] mov[i]]检查是否可以追着蛇尾运动，即蛇头和蛇尾间是有路径的，为的是避免蛇头陷入死路 。虚拟操作，在tmpboard,tmpsnake中进行 。
def is_tail_inside():global tmpboard, tmpsnake, food, tmpsnake_sizetmpboard[tmpsnake[tmpsnake_size-1]] = 0 # 虚拟地将蛇尾变为食物(因为是虚拟的，所以在tmpsnake,tmpboard中进行)tmpboard[food] = SNAKE # 放置食物的地方，看成蛇身result = board_BFS(tmpsnake[tmpsnake_size-1], tmpsnake, tmpboard) # 求得每个位置到蛇尾的路径长度for i in range(4): # 如果蛇头和蛇尾紧挨着，则返回False 。即不能follow_tail，追着蛇尾运动了if is_move_possible(tmpsnake[HEAD], mov[i]) and tmpsnake[HEAD] mov[i]==tmpsnake[tmpsnake_size-1] and tmpsnake_size>3:result = Falsereturn result让蛇头朝着蛇尾运行一步，不管蛇身阻挡，朝蛇尾方向运行 。‘
def follow_tail():global tmpboard, tmpsnake, food, tmpsnake_sizetmpsnake_size = snake_sizetmpsnake = snake[:]board_reset(tmpsnake, tmpsnake_size, tmpboard) # 重置虚拟boardtmpboard[tmpsnake[tmpsnake_size-1]] = FOOD # 让蛇尾成为食物tmpboard[food] = SNAKE # 让食物的地方变成蛇身board_BFS(tmpsnake[tmpsnake_size-1], tmpsnake, tmpboard) # 求得各个位置到达蛇尾的路径长度tmpboard[tmpsnake[tmpsnake_size-1]] = SNAKE # 还原蛇尾return choose_longest_safe_move(tmpsnake, tmpboard) # 返回运行方向(让蛇头运动1步)在各种方案都不行时，随便找一个可行的方向来走(1步)
def any_possible_move():global food , snake, snake_size, boardbest_move = ERRboard_reset(snake, snake_size, board)board_BFS(food, snake, board)min = SNAKEfor i in range(4):if is_move_possible(snake[HEAD], mov[i]) and board[snake[HEAD] mov[i]]转换数组函数
def shift_array(arr, size):for i in range(size, 0, -1):arr[i] = arr[i-1]def new_food():#随机函数生成新的食物global food, snake_sizecell_free = Falsewhile not cell_free:w = random.randint(1, WIDTH-2)h = random.randint(1, HEIGHT-2)food = WIDTH*hwcell_free = is_cell_free(food, snake_size, snake)pygame.draw.rect(playSurface,redColour,Rect(18*(food//WIDTH), 18*(food%WIDTH),18,18))真正的蛇在这个函数中，朝pbest_move走1步 。
def make_move(pbest_move): global snake, board, snake_size, score shift_array(snake, snake_size) snake[HEAD]= pbest_movep = snake[HEAD]for body in snake:#画蛇，身体，头，尾pygame.draw.rect(playSurface,whiteColour,Rect(18*(body//WIDTH), 18*(body%WIDTH),18,18))pygame.draw.rect(playSurface,greenColour,Rect(18*(snake[snake_size-1]//WIDTH),18*(snake[snake_size-1]%WIDTH),18,18))pygame.draw.rect(playSurface,headColour,Rect(18*(p//WIDTH), 18*(p%WIDTH),18,18))#下面一行是把初始情况会出现的第一个白块bug填掉pygame.draw.rect(playSurface,(255,255,0),Rect(0,0,18,18))# 刷新pygame显示层pygame.display.flip()# 如果新加入的蛇头就是食物的位置# 蛇长加1，产生新的食物，重置board(因为原来那些路径长度已经用不上了)if snake[HEAD] == food:board[snake[HEAD]] = SNAKE # 新的蛇头snake_size= 1score= 1if snake_size < FIELD_SIZE: new_food()else: # 如果新加入的蛇头不是食物的位置board[snake[HEAD]] = SNAKE # 新的蛇头board[snake[snake_size]] = UNDEFINED # 蛇尾变为UNDEFINED，黑色pygame.draw.rect(playSurface,blackColour,Rect(18*(snake[snake_size]//WIDTH),18*(snake[snake_size]%WIDTH),18,18))# 刷新pygame显示层pygame.display.flip()