操作系统 磁盘调度---扫描（SCAN）算法 （电梯调度算法）（C++实现 操作系统实验）

不仅考虑到欲访问的磁道与当前磁道间的距离，更优先考虑的是磁头当前的移动方向，当磁头正在自里向外移动时，SCAN算法所考虑的下一个访问对象应是该磁头自里向外方向上距离最近的那个，直至扫描完最外面的磁头，然后方向变为自外向里扫描

#include
#include
#include
#include
#include

using namespace std;
int n;
int start;
int xb;
typedef pair p;
vector
 v;
vector seq;
const int INF = 0x3f3f3f3f;
double avgfind;

int main() {
   
   cout << "请输入磁道个数：" << "n";
    cin >> n;
    int temp = n;
    cout << "请输入开始磁道号：" << "n";
    cin >> start;

    int x;
    cout << "请依次输入" << n << "个磁道号" << "n";
    for(int i = 1; i <= n; i ++) {
        cin >> x;
        seq.push_back(x);
    }
    sort(seq.begin(), seq.end());

    if(seq[0] > start) {
        v.push_back({seq[0], abs(seq[0] - start)});
        avgfind += abs(seq[0] - start);
        start = seq[0];

        xb = 1;

        for(int i = xb; i < seq.size(); i ++) {
            v.push_back({seq[i], abs(seq[i] - start)});
            avgfind += abs(seq[i] - start);
            start = seq[i];
        }
    } 
    else if(seq[n - 1] < start) {
        v.push_back({seq[n - 1], abs(start - seq[n - 1])});
        avgfind += abs(start - seq[n - 1]);
        xb = n - 2;
        start = seq[n - 1];

        for(int i = xb; i >= 0; i --) {
            v.push_back({seq[i], abs(seq[i] - start)});
            avgfind += abs(seq[i] - start);
            start = seq[i];
        }

    } else {
        for(int i = 0; i < seq.size() - 1; i ++) {
        if(seq[i + 1] > start && seq[i] < start) {
            v.push_back({seq[i + 1], abs(seq[i + 1] - start)});
            avgfind += abs(seq[i + 1] - start);
            start = seq[i + 1];
            xb = (i + 2 > seq.size()) ? seq.size() : (i + 2);
            break;
        }
    }
         for(int i = xb; i < seq.size(); i ++) {
            v.push_back({seq[i], abs(seq[i] - start)});
            avgfind += abs(seq[i] - start);
            start = seq[i];
        }
        for(int i = xb - 2; i >= 0; i --) {
            v.push_back({seq[i], abs(seq[i] - start)});
            avgfind += abs(seq[i] - start);
            start = seq[i];
        }
    }

        
    cout << "n";
    cout << "磁道号t移动距离" << "n";
    for(int i = 0; i < v.size(); i ++) {
        cout << v[i].first << "t" << v[i].second << "n";
    }
    cout << "平均寻道长度：" << "t";
    printf("%.2lf", avgfind / temp);
    
   return 0;
}