snake-draft.py

# coding: utf-8

import curses
from curses import KEY_RIGHT, KEY_LEFT, KEY_UP, KEY_DOWN
from random import randint

# 蛇运动的场地长宽
HEIGHT = 10
WIDTH = 20
FIELD_SIZE = HEIGHT * WIDTH

# 蛇头总是位于snake数组的第一个元素
HEAD = 0

# 用来代表不同东西的数字，由于矩阵上每个格子会处理成到达食物的路径长度，
# 因此这三个变量间需要有足够大的间隔(>HEIGHT*WIDTH)
FOOD = 0
UNDEFINED = (HEIGHT + 1) * (WIDTH + 1)
SNAKE = 2 * UNDEFINED

# 由于snake是一维数组，所以对应元素直接加上以下值就表示向四个方向移动
LEFT = -1
RIGHT = 1
UP = -WIDTH
DOWN = WIDTH

# 错误码
ERR = -1111

# 用一维数组来表示二维的东西
# board表示蛇运动的矩形场地
# 初始化蛇头在(1,1)的地方，第0行，HEIGHT行，第0列，WIDTH列为围墙，不可用
# 初始蛇长度为1
board = [0] * FIELD_SIZE
snake = [0] * (FIELD_SIZE+1)
snake[HEAD] = 1*WIDTH+1
snake_size = 1
# 与上面变量对应的临时变量，蛇试探性地移动时使用
tmpboard = [0] * FIELD_SIZE
tmpsnake = [0] * (FIELD_SIZE+1)
tmpsnake[HEAD] = 1*WIDTH+1
tmpsnake_size = 1

# food:食物位置(0~FIELD_SIZE-1),初始在(3, 3)
# best_move: 运动方向
food = 3 * WIDTH + 3
best_move = ERR

# 运动方向数组
mov = [LEFT, RIGHT, UP, DOWN]
# 接收到的键 和 分数
key = KEY_RIGHT                                                    
score = 1 #分数也表示蛇长

# 检查一个cell有没有被蛇身覆盖，没有覆盖则为free，返回true
def is_cell_free(idx, psize, psnake):
    #return not (idx in psnake[:]) #错！psnake后面还有很多没用上的单元
    for i in xrange(psize):
        if idx == psnake[i]: return False
    return True
    

# 检查某个位置idx是否可向move方向运动
def is_move_possible(idx, move):
    flag = False
    if move == LEFT:
        flag = True if idx%WIDTH > 1 else False
    elif move == RIGHT:
        flag = True if idx%WIDTH < (WIDTH-2) else False
    elif move == UP:
        flag = True if idx > (2*WIDTH-1) else False # 即idx/WIDTH > 1
    elif move == DOWN:
        flag = True if idx < (FIELD_SIZE-2*WIDTH) else False # 即idx/WIDTH < HEIGHT-2
    return flag
# 重置board
# board_refresh后，UNDEFINED值都变为了到达食物的路径长度
# 如需要还原，则要重置它
def board_reset(psnake, psize, pboard):
    for i in xrange(FIELD_SIZE):
       # f.write('hello ' + str(len(pboard)) +' ' +str(i)+'\n')
        if i == food:
            pboard[i] = FOOD
        elif is_cell_free(i, psize, psnake): # 该位置为空
            pboard[i] = UNDEFINED
        else: # 该位置为蛇身
            pboard[i] = SNAKE
    
# def board_refresh(pfood, psnake, pboard):
#     board_changed = True
#     found = False
#     while board_changed: # 一直更新board，直到每个格子上的数都对应到达食物的步数，不能再改变为止
#         board_changed = False
#         for i in xrange(FIELD_SIZE):
#             if pboard[i] < SNAKE: 
#                 min = pboard[i]
#                 for j in xrange(4):
#                     if is_move_possible(i, mov[j]) and pboard[i+mov[j]] < min:
#                         min = pboard[i+mov[j]]
#                 if pboard[i] > min+1:
#                     pboard[i] = min + 1
#                     board_changed = True

#         if ~board_changed: break # 不再改变，退出
#         board_changed = False

#         for i in xrange(FIELD_SIZE-1, -1, -1): # [FIELD_SIZE-1, 0]
#             if pboard[i] < SNAKE:
#                 min = pboard[i]
#                 for j in xrange(4):
#                     if is_move_possible(i, mov[j]) and pboard[i+mov[j]] < min:
#                         min = pboard[i+mov[j]]
#                 if pboard[i] > min+1:
#                     pboard[i] = min + 1
#                     board_changed = True
#     for i in xrange(4):
#         if is_move_possible(psnake[HEAD], mov[i]) and pboard[psnake[HEAD]+mov[i]]<UNDEFINED:
#             flag = True

#     return flag

# 广度优先搜索遍历整个board，
# 计算出board中每个非SNAKE元素到达食物的路径长度
def board_refresh(pfood, psnake, pboard):
    queue = []
    queue.append(pfood)
    inqueue = [0] * FIELD_SIZE
    found = False
    # while循环结束后，除了蛇的身体，
    # 其它每个方格中的数字代码从它到食物的路径长度
    #f.write('bfs begin:\n')
    while len(queue)!=0: 
        idx = queue.pop(0)
        if inqueue[idx] == 1: continue
        #f.write(str(idx)+'\n')
        inqueue[idx] = 1
        for i in xrange(4):
            if is_move_possible(idx, mov[i]):
                if idx + mov[i] == psnake[HEAD]:
                    found = True
                if pboard[idx+mov[i]] < SNAKE: # 如果该点不是蛇的身体
                    
                    if pboard[idx+mov[i]] > pboard[idx]+1:
                        pboard[idx+mov[i]] = pboard[idx] + 1
                    if inqueue[idx+mov[i]] == 0:
                        queue.append(idx+mov[i])

    #f.write('bfs end\n')
    #f.write('found: ' + str(found) +'\n')
    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 = ERR
    min = SNAKE
    for i in xrange(4):
        if is_move_possible(psnake[HEAD], mov[i]) and pboard[psnake[HEAD]+mov[i]]<min:
            min = pboard[psnake[HEAD]+mov[i]]
            best_move = mov[i]
    return best_move

# 从蛇头开始，根据board中元素值，
# 从蛇头周围4个领域点中选择最远路径
def choose_longest_safe_move(psnake, pboard):
    best_move = ERR
    max = -1
    for i in xrange(4):
        if is_move_possible(psnake[HEAD], mov[i]) and pboard[psnake[HEAD]+mov[i]]<UNDEFINED and pboard[psnake[HEAD]+mov[i]]>max:
            max = pboard[psnake[HEAD]+mov[i]]
            best_move = mov[i]
    return best_move

# 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_size
    tmpboard[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_refresh(tmpsnake[tmpsnake_size-1], tmpsnake, tmpboard) # 求得每个位置到蛇尾的路径长度
    for i in xrange(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 = False
    return 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_size
    tmpsnake_size = snake_size
    tmpsnake = snake[:]
    board_reset(tmpsnake, tmpsnake_size, tmpboard) # 重置虚拟board
    tmpboard[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_refresh(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)
    return choose_longest_safe_move(tmpsnake, tmpboard)

# 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, board
    best_move = ERR
    board_reset(snake, snake_size, board)
    board_refresh(food, snake, board)
    min = SNAKE

    for i in xrange(4):
        if is_move_possible(snake[HEAD], mov[i]) and board[snake[HEAD]+mov[i]]<min:
            min = board[snake[HEAD]+mov[i]]
            best_move = mov[i]
    return best_move

def shift_array(arr, size):
    for i in xrange(size, 0, -1):
        arr[i] = arr[i-1]

def new_food():
    global food, snake_size
    if snake_size >= FIELD_SIZE-1: return
    cell_free = False
    while not cell_free:
        w = randint(1, WIDTH-2)
        h = randint(1, HEIGHT-2)
        food = h * WIDTH + w
        cell_free = is_cell_free(food, snake_size, snake)
    win.addch(food/WIDTH, food%WIDTH, '@')

# 真正的蛇在这个函数中，朝pbest_move走1步
def make_move(pbest_move):
    global key, snake, board, snake_size, score
    shift_array(snake, snake_size)
    snake[HEAD] += pbest_move
    

    # 按esc退出，getch同时保证绘图的流畅性，没有它只会看到最终结果
    win.timeout(10)
    event = win.getch()
    key = key if event == -1 else event
    if key == 27: return

    p = snake[HEAD]
    win.addch(p/WIDTH, p%WIDTH, '*')

    
    # 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 += 1
        score += 1
        if snake_size < FIELD_SIZE: new_food()
        #board_reset(snake, board) # 
        #return True
    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 # 蛇尾变为空格
        win.addch(snake[snake_size]/WIDTH, snake[snake_size]%WIDTH, ' ')
        #return False
    # test 打印tmpboard
    for i in xrange(HEIGHT):
        for j in xrange(WIDTH):
            k = board[i*WIDTH+j]
            f.write(str(k)+' ')
        f.write('\n')
    # print symbol
    for i in xrange(HEIGHT):
        for j in xrange(WIDTH):
            k = board[i*WIDTH+j]
            if k == UNDEFINED:
                f.write('# ')
            elif k == SNAKE:
                if i*WIDTH+j == snake[HEAD]:
                    f.write('+ ') # 蛇头
                elif i*WIDTH+j == snake[snake_size-1]:
                    f.write('- ') # 蛇尾
                else:
                    f.write('* ')
            else:
                f.write(str(k)+' ')
        f.write('\n')
    f.write('\n')

# 虚拟地运行一次，然后在调用处检查这次运行可否可行
# 可行才真实运行。
# 虚拟运行吃到食物后，得到虚拟下蛇在board的位置
def virtual_shortest_move():
    global snake, board, snake_size, tmpsnake, tmpboard, tmpsnake_size, food
    #f.write('i am in virtual\n')
    tmpsnake_size = snake_size
    tmpsnake = snake[:] # 如果直接tmpsnake=snake，则两者指向同一处内存
    tmpboard = board[:] # board中已经是各位置到达食物的路径长度了，不用再计算
    board_reset(tmpsnake, tmpsnake_size, tmpboard)
    

    # test 打印tmpboard
    # for i in xrange(HEIGHT):
    #     for j in xrange(WIDTH):
    #         k = tmpboard[i*WIDTH+j]
    #         f.write(str(k)+' ')
    #     f.write('\n')
    
    food_eated = False
    while not food_eated:
        board_refresh(food, tmpsnake, tmpboard)    
        move = choose_shortest_safe_move(tmpsnake, tmpboard)
        shift_array(tmpsnake, tmpsnake_size)
        tmpsnake[HEAD] += move # 在蛇头前加入一个新的位置
        #f.write('snake head: '+str(tmpsnake[HEAD])+'\n')
        # 如果新加入的蛇头的位置正好是食物的位置
        # 则长度加1，重置board，食物那个位置变为蛇的一部分(SNAKE)
        if tmpsnake[HEAD] == food:
            tmpsnake_size += 1
            board_reset(tmpsnake, tmpsnake_size, tmpboard) # 虚拟运行后，蛇在board的位置(label101010)
            tmpboard[food] = SNAKE
            food_eated = True
        else: # 如果蛇头不是食物的位置，则新加入的位置为蛇头，最后一个变为空格
            tmpboard[tmpsnake[HEAD]] = SNAKE
            tmpboard[tmpsnake[tmpsnake_size]] = UNDEFINED
    #f.write('i am out virtual\n')

# 如果蛇与食物间有路径，则调用本函数
def find_safe_way():
    global snake, board
    safe_move = ERR
    # 虚拟地运行一次，因为已经确保蛇与食物间有路径，所以执行有效
    # 运行后得到虚拟下蛇在board中的位置，即tmpboard，见label101010
    virtual_shortest_move() # 该函数唯一调用处
    if is_tail_inside(): # 如果虚拟运行后，蛇头蛇尾间有通路，则选最短路运行(1步)
        return choose_shortest_safe_move(snake, board)
    safe_move = follow_tail() # 否则虚拟地follow_tail 1步，如果可以做到，返回true
    return safe_move


curses.initscr()
win = curses.newwin(HEIGHT, WIDTH, 0, 0)
win.keypad(1)
curses.noecho()
curses.curs_set(0)
win.border(0)
win.nodelay(1)
win.addch(food/WIDTH, food%WIDTH, '@')

f = file('log', 'w')
    
while key != 27:
    win.border(0)
    win.addstr(0, 2, 's:' + str(score) + ' ')               
    #win.addstr(0, WIDTH/2-3, ' SNAKE ')                                  
    win.timeout(10)
    # 接收键盘输入，同时也使显示流畅
    event = win.getch()
    key = key if event == -1 else event
    if snake_size >= FIELD_SIZE: continue
    # 重置矩阵
    board_reset(snake, snake_size, board)
    
    # 如果蛇可以吃到食物，board_refresh返回true
    # 并且board中除了蛇身(=SNAKE)，其它的元素值表示从该点运动到食物的最短路径长
    if board_refresh(food, snake, board):
        best_move  = find_safe_way() # find_safe_way的唯一调用处
        f.write('find safe way: ' + str(best_move) + '\n')
    else:
        best_move = follow_tail()
        f.write('follow tail: ' + str(best_move) +'\n')
            
    if best_move == ERR:
        best_move = any_possible_move()
        f.write('any possible move: ' + str(best_move) + '\n')
    # 上面一次思考，只得出一个方向，运行一步
    if best_move != ERR: make_move(best_move)   
    else: break        
        
f.close()
curses.endwin()
print("\nScore - " + str(score))