操作系统 磁盘调度---循环扫描（CSCAN）算法（C++实现 操作系统实验）_循环扫描调度算法

思路：

自里向外移动，当磁头移到最外的磁道并访问后，磁头立即返回到最里的欲访问磁道，即将最小磁道号紧接着最大磁道号构成循环，进行循环扫描

代码如下：

#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
#include<cmath>
 
using namespace std;
int n;
int start;
int xb;
typedef pair<int, int> p;
vector<p> v;
vector<int> 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 = 0; i <= xb - 2; 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;
}