通过编写和调试磁盘调度程序，加深对磁盘调度算法的理解，进一步掌握先来先服务FCFS，最短寻道时间优先SSTF，SCAN和循环SCAN算法的实现方法。并写出相关详细代码

通过编写和调试磁盘调度程序，你可以亲手构建和理解这些经典的磁盘调度算法。下面是一个简单的Python示例，展示如何实现FCFS (先来先服务)，SSTF (最短寻道时间优先)，SCAN 和循环SCAN算法：

首先，我们假设有一个磁盘请求队列（可以用列表表示），每个元素包含磁道编号和请求时间：

class DiskRequest:
    def __init__(self, track_id, request_time):
        self.track_id = track_id
        self.request_time = request_time

requests = [DiskRequest(track_id, time) for track_id, time in enumerate(range(1, N+1))]

start_track = 0  # 开始磁道
direction = "forward"  # 默认正向扫描

然后我们可以为这些算法编写单独的函数：

1. 先来先服务 (FCFS)

def fcfsscheduling(requests, start, direction):
    total_distance = 0
    sorted_requests = sorted(requests, key=lambda r: r.request_time)
    
    for req in sorted_requests:
        total_distance += abs(req.track_id - start)
        start = req.track_id
        
    return total_distance

2. 最短寻道时间优先 (SSTF)

def sstfscheduling(requests, start, direction):
    if not requests or start >= len(requests):
        return 0
    
    min_dist = float('inf')
    next_track = None
    for req in requests:
        dist = abs(req.track_id - start)
        if dist < min_dist:
            min_dist = dist
            next_track = req.track_id
            
    start = next_track
    return min_dist + sstfscheduling(requests[requests.index(next_track)+1:], start, direction)

3. 扫描 (SCAN)

def scanscheduling(requests, start, direction):
    total_distance = 0
    for req in requests:
        total_distance += abs(req.track_id - start)
        start = max(start, req.track_id) if direction == "forward" else min(start, req.track_id)
        
    return total_distance

4. 循环扫描 (Cycle SCAN)

def cycscanscheduling(requests, start, direction):
    total_distance = 0
    for _ in range(len(requests)):
        current_track = start
        for req in requests:
            total_distance += abs(req.track_id - current_track)
            current_track = req.track_id
        start = current_track if direction == "forward" else start  # 切换方向
            
    return total_distance

最后，在`main`函数中整合上述算法，并计算平均寻道长度：

def main():
    print(f"FCFS Average Seek Length: {fcfsscheduling(requests, start_track, direction)}")
    print(f"SSTF Average Seek Length: {sstfscheduling(requests, start_track, direction)}")
    print(f"SCAN Average Seek Length: {scanscheduling(requests, start_track, direction)}")
    print(f"Cycle SCAN Average Seek Length: {cycscanscheduling(requests, start_track, direction)}")

if __name__ == "__main__":
    main()

记得根据你的实际需求调整代码，比如读取磁道请求序列文件等。运行这个程序，你就可以看到每个算法的平均寻道长度了。同时，注意对算法的时间复杂性和空间复杂性进行讨论和优化。