c++实现SCAN算法

SCAN算法又称电梯算法，是一种磁盘调度算法，常用于操作系统中磁盘调度的实现。其思想是：磁头按一个方向移动，直到到达磁盘的最边缘，然后改变方向，继续移动，直到访问完所有的磁道。

下面是C++实现SCAN算法的示例代码：

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

int main()
{
    int head, n;
    cout << "Enter the initial position of head: ";
    cin >> head;
    cout << "Enter the number of requests: ";
    cin >> n;

    vector<int> requests(n);
    cout << "Enter the requests: ";
    for (int i = 0; i < n; i++) {
        cin >> requests[i];
    }

    sort(requests.begin(), requests.end());

    int total_moves = 0;
    int current_pos = head;
    int direction = 1; // 1 for moving towards higher tracks, -1 for moving towards lower tracks

    auto it = lower_bound(requests.begin(), requests.end(), current_pos);
    if (it != requests.end()) {
        total_moves += abs(*it - current_pos);
        current_pos = *it;
        requests.erase(it);
    }

    while (!requests.empty()) {
        if (direction == 1) {
            it = upper_bound(requests.begin(), requests.end(), current_pos);
            if (it != requests.end()) {
                total_moves += abs(*it - current_pos);
                current_pos = *it;
                requests.erase(it);
            } else {
                direction = -1;
                it = upper_bound(requests.begin(), requests.end(), current_pos);
                if (it != requests.begin()) {
                    it--;
                    total_moves += abs(*it - current_pos);
                    current_pos = *it;
                    requests.erase(it);
                }
            }
        } else {
            it = lower_bound(requests.begin(), requests.end(), current_pos, greater<int>());
            if (it != requests.end()) {
                total_moves += abs(*it - current_pos);
                current_pos = *it;
                requests.erase(it);
            } else {
                direction = 1;
                it = lower_bound(requests.begin(), requests.end(), current_pos, greater<int>());
                if (it != requests.end()) {
                    total_moves += abs(*it - current_pos);
                    current_pos = *it;
                    requests.erase(it);
                }
            }
        }
    }

    cout << "Total head movements: " << total_moves << endl;

    return 0;
}

代码中使用了STL中的vector容器和算法库，实现了SCAN算法的主要逻辑。首先输入磁头的初始位置和请求序列，对请求序列进行排序，然后依次处理每个请求，计算磁头移动的距离，最后输出总的磁头移动距离。

需要注意的是，代码中使用了lower_bound和upper_bound函数来查找请求序列中离当前磁头位置最近的请求，具体使用方法可以参考STL库的相关文档。