写出FCFS SSTF SCAN CSCAN java代码

以下是FCFS、SSTF、SCAN、CSCAN算法的Java实现示例：

FCFS：

public static int FCFS(int[] requests, int head) {
    int total = 0;
    int cur = head;
    for (int i = 0; i < requests.length; i++) {
        total += Math.abs(cur - requests[i]);
        cur = requests[i];
    }
    return total;
}

SSTF：

public static int SSTF(int[] requests, int head) {
    int total = 0;
    int cur = head;
    boolean[] visited = new boolean[requests.length];
    Arrays.fill(visited, false);
    for (int i = 0; i < requests.length; i++) {
        int minDist = Integer.MAX_VALUE;
        int index = -1;
        for (int j = 0; j < requests.length; j++) {
            if (!visited[j]) {
                int dist = Math.abs(cur - requests[j]);
                if (dist < minDist) {
                    minDist = dist;
                    index = j;
                }
            }
        }
        visited[index] = true;
        total += minDist;
        cur = requests[index];
    }
    return total;
}

SCAN：

public static int SCAN(int[] requests, int head, int max) {
    int total = 0;
    int cur = head;
    boolean left = true;
    Arrays.sort(requests);
    int index = Arrays.binarySearch(requests, cur);
    if (index < 0) {
        index = -index - 1;
    }
    while (index < requests.length && requests[index] <= cur) {
        index++;
    }
    if (index == requests.length) {
        left = false;
        index--;
    }
    while (true) {
        if (left) {
            total += cur;
            if (index == 0) {
                total += requests[index];
                cur = requests[index];
                left = false;
                index++;
            } else {
                total += cur - requests[index - 1];
                cur = requests[index - 1];
                index--;
            }
        } else {
            total += max - cur;
            if (index == requests.length - 1) {
                total += max - requests[index];
                cur = requests[index];
                left = true;
                index--;
            } else {
                total += requests[index + 1] - cur;
                cur = requests[index + 1];
                index++;
            }
        }
        if (index < 0 || index >= requests.length) {
            break;
        }
    }
    return total;
}

CSCAN：

public static int CSCAN(int[] requests, int head, int max) {
    int total = 0;
    int cur = head;
    boolean left = true;
    Arrays.sort(requests);
    int index = Arrays.binarySearch(requests, cur);
    if (index < 0) {
        index = -index - 1;
    }
    while (index < requests.length && requests[index] <= cur) {
        index++;
    }
    if (index == requests.length) {
        index = 0;
    }
    while (true) {
        if (left) {
            total += cur;
            if (index == requests.length) {
                total += max - cur;
                cur = 0;
                index = 0;
            } else {
                total += cur - requests[index - 1];
                cur = requests[index - 1];
            }
            left = false;
        } else {
            total += max - cur;
            if (index == 0) {
                total += max - requests[requests.length - 1];
                cur = max;
                index = requests.length;
            } else {
                total += requests[index] - cur;
                cur = requests[index];
            }
            left = true;
        }
        if (index == requests.length && !left) {
            break;
        }
    }
    return total;
}