编写程序模拟银行家算法

银行家算法是一种用于避免死锁的算法，它通过动态地检查系统资源的分配情况来判断是否可以分配资源，避免了死锁的出现。下面是一个简单的银行家算法的实现：

# 银行家算法
class Banker:
    def __init__(self, available, max_need, allocation):
        self.available = available  # 可用资源数
        self.max_need = max_need  # 进程最大需求量
        self.allocation = allocation  # 进程已分配资源数
        self.process_num = len(max_need)  # 进程数
        self.request_num = None  # 请求资源数
        self.process_id = None  # 请求进程ID

    def safety(self):
        # 安全性检查
        work = self.available.copy()  # 可用资源数
        finish = [False] * self.process_num  # 进程完成状态
        need = [[self.max_need[i][j] - self.allocation[i][j] for j in range(len(self.available))] for i in range(self.process_num)]  # 进程还需资源数

        # 遍历进程
        while True:
            # 遍历进程，查找符合条件的进程
            flag = False
            for i in range(self.process_num):
                if not finish[i] and all([need[i][j] <= work[j] for j in range(len(self.available))]):
                    work = [work[j] + self.allocation[i][j] for j in range(len(self.available))]
                    finish[i] = True
                    flag = True

            if not flag:
                break

        return all(finish)

    def request_resources(self, process_id, request_num):
        # 进程申请资源
        self.process_id = process_id
        self.request_num = request_num

        if any([request_num[i] > self.max_need[process_id][i] - self.allocation[process_id][i] for i in range(len(self.available))]):
            # 请求资源数大于进程最大需求量
            print("Request exceeds maximum need!")
            return False

        if any([request_num[i] > self.available[i] for i in range(len(self.available))]):
            # 请求资源数大于可用资源数
            print("Not enough resources available!")
            return False

        # 模拟分配资源
        self.available = [self.available[i] - request_num[i] for i in range(len(self.available))]
        self.allocation[process_id] = [self.allocation[process_id][i] + request_num[i] for i in range(len(self.available))]

        if not self.safety():
            # 分配资源后不安全
            print("Unsafe state!")
            self.available = [self.available[i] + request_num[i] for i in range(len(self.available))]
            self.allocation[process_id] = [self.allocation[process_id][i] - request_num[i] for i in range(len(self.available))]
            return False

        return True

    def release_resources(self, process_id):
        # 进程释放资源
        self.available = [self.available[i] + self.allocation[process_id][i] for i in range(len(self.available))]
        self.allocation[process_id] = [0] * len(self.available)

以上是一个简单的银行家算法的实现，其中 `available` 表示可用资源数，`max_need` 表示每个进程的最大需求量，`allocation` 表示每个进程已分配的资源数。`safety` 方法用于检查系统是否处于安全状态，`request_resources` 方法用于进程申请资源，`release_resources` 方法用于进程释放资源。