用python编写一个字符界面的五子棋人机对战程序，游戏难度中等

好的，下面是代码实现：

import os

# 初始化棋盘
def init_board():
    board = []
    for i in range(0, 15):
        row = ["+" for i in range(0, 15)]
        board.append(row)
    return board

# 显示棋盘
def display_board(board):
    os.system("clear")
    print("  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15")
    for i in range(0, 15):
        print(chr(i+ord("a")), end=" ")
        for j in range(0, 15):
            print(board[i][j], end=" ")
        print()

# 判断是否下在了棋盘内
def is_valid_location(board, row, col):
    if row < 0 or row >= len(board) or col < 0 or col >= len(board[0]):
        return False
    if board[row][col] != "+":
        return False
    return True

# 下棋
def make_move(board, row, col, player):
    if is_valid_location(board, row, col):
        board[row][col] = player
        return True
    return False

# 判断是否获胜
def check_win(board, player):
    for i in range(0, 15):
        for j in range(0, 11):
            if board[i][j:j+5] == [player]*5:
                return True
    for i in range(0, 11):
        for j in range(0, 15):
            if [board[i+k][j] for k in range(0, 5)] == [player]*5:
                return True
    for i in range(0, 11):
        for j in range(0, 11):
            if [board[i+k][j+k] for k in range(0, 5)] == [player]*5:
                return True
    for i in range(0, 11):
        for j in range(4, 15):
            if [board[i+k][j-k] for k in range(0, 5)] == [player]*5:
                return True
    return False

# 人机对战
def play():
    board = init_board()
    display_board(board)
    player = "X"
    while True:
        if player == "X":
            row = input("请落子(如a1):")
            row = ord(row[0]) - ord("a")
            col = int(row[1:]) - 1
        else:
            row, col = get_computer_move(board)
        if make_move(board, row, col, player):
            display_board(board)
            if check_win(board, player):
                print("恭喜", player, "获胜！")
                break
            if player == "X":
                player = "O"
            else:
                player = "X"

# 计算AI的落子位置
def get_computer_move(board):
    for i in range(0, 15):
        for j in range(0, 15):
            if board[i][j] == "+":
                if check_win_by_location(board, i, j, "O"):
                    return i, j
    for i in range(0, 15):
        for j in range(0, 15):
            if board[i][j] == "+":
                if check_win_by_location(board, i, j, "X"):
                    return i, j
    for i in range(0, 15):
        for j in range(0, 15):
            if board[i][j] == "+":
                if check_live_three_by_location(board, i, j, "O"):
                    return i, j
    for i in range(0, 15):
        for j in range(0, 15):
            if board[i][j] == "+":
                if check_live_three_by_location(board, i, j, "X"):
                    return i, j
    for i in range(0, 15):
        for j in range(0, 15):
            if board[i][j] == "+":
                if check_live_two_by_location(board, i, j, "O"):
                    return i, j
    for i in range(0, 15):
        for j in range(0, 15):
            if board[i][j] == "+":
                if check_live_two_by_location(board, i, j, "X"):
                    return i, j
    while True:
        row, col = random.randint(0, 14), random.randint(0, 14)
        if board[row][col] == "+":
            return row, col

# 判断在某个位置能否获胜
def check_win_by_location(board, row, col, player):
    board[row][col] = player
    win = check_win(board, player)
    board[row][col] = "+"
    return win

# 判断在某个位置是否形成活三棋型
def check_live_three_by_location(board, row, col, player):
    board[row][col] = player
    live_three = False
    for i in range(0, 15):
        for j in range(0, 15):
            if board[i][j] == "+":
                board[i][j] = "O" if player == "X" else "X"
                if check_win_by_location(board, i, j, player):
                    live_three = True
                board[i][j] = "+"
    board[row][col] = "+"
    return live_three

# 判断在某个位置是否形成活二棋型
def check_live_two_by_location(board, row, col, player):
    board[row][col] = player
    live_two = False
    for i in range(0, 15):
        for j in range(0, 15):
            if board[i][j] == "+":
                board[i][j] = "O" if player == "X" else "X"
                if check_live_three_by_location(board, i, j, player):
                    live_two = True
                board[i][j] = "+"
    board[row][col] = "+"
    return live_two

play()

这个程序使用了一些基本的算法来实现AI的落子位置计算，包括：

1. 判断在某个位置能否获胜
2. 判断在某个位置是否形成活三棋型
3. 判断在某个位置是否形成活二棋型

这些算法都是基于五子棋的规则和常识来实现的，当然也可以使用更加高级的算法来实现，比如蒙特卡罗树搜索等。