用c++实现银行家算法

银行家算法是一种用于避免系统资源死锁的算法，以下是一个简单的 C++ 实现：

#include <iostream>
#include <vector>

using namespace std;

const int MAX_PROCESS = 100;
const int MAX_RESOURCE = 100;

int available[MAX_RESOURCE];
int allocation[MAX_PROCESS][MAX_RESOURCE];
int max_need[MAX_PROCESS][MAX_RESOURCE];
int need[MAX_PROCESS][MAX_RESOURCE];
bool finish[MAX_PROCESS];

int num_process, num_resource;

bool is_safe() {
    vector<int> work(available, available + num_resource);
    vector<bool> finished(num_process, false);

    bool changed = true;
    while (changed) {
        changed = false;
        for (int i = 0; i < num_process; i++) {
            if (!finished[i]) {
                bool possible = true;
                for (int j = 0; j < num_resource; j++) {
                    if (need[i][j] > work[j]) {
                        possible = false;
                        break;
                    }
                }

                if (possible) {
                    finished[i] = true;
                    changed = true;
                    for (int j = 0; j < num_resource; j++) {
                        work[j] += allocation[i][j];
                    }
                }
            }
        }
    }

    for (int i = 0; i < num_process; i++) {
        if (!finished[i]) {
            return false;
        }
    }

    return true;
}

int main() {
    cout << "Enter the number of processes: ";
    cin >> num_process;

    cout << "Enter the number of resources: ";
    cin >> num_resource;

    cout << "Enter the available resources: ";
    for (int i = 0; i < num_resource; i++) {
        cin >> available[i];
    }

    cout << "Enter the allocation matrix:\n";
    for (int i = 0; i < num_process; i++) {
        for (int j = 0; j < num_resource; j++) {
            cin >> allocation[i][j];
        }
    }

    cout << "Enter the maximum need matrix:\n";
    for (int i = 0; i < num_process; i++) {
        for (int j = 0; j < num_resource; j++) {
            cin >> max_need[i][j];
            need[i][j] = max_need[i][j] - allocation[i][j];
        }
    }

    if (is_safe()) {
        cout << "The system is in a safe state.\n";
    } else {
        cout << "The system is not in a safe state.\n";
    }

    return 0;
}

在代码中，`available` 数组表示当前可用的资源数量，`allocation` 数组表示每个进程已经分配的资源，`max_need` 数组表示每个进程最多需要的资源，`need` 数组表示每个进程还需要的资源数量，`finish` 数组表示每个进程是否已经执行完毕。`is_safe` 函数用于判断系统是否处于安全状态，如果是则返回 true，否则返回 false。

在程序中，首先需要输入进程数、资源数、可用资源数量、分配矩阵和最大需求矩阵，然后调用 `is_safe` 函数进行判断。如果系统处于安全状态，则输出 "The system is in a safe state."，否则输出 "The system is not in a safe state."