Java data structure and algorithm: detailed explanation of practical cases

int[] scores = {90, 85, 78, 95, 82};

class Node {
    int value;
    Node next;
}

class Queue {
    Node head;
    Node tail;

    public void enqueue(int value) {
        Node newNode = new Node();
        newNode.value = value;
        if (head == null) {
            head = newNode;
            tail = newNode;
        } else {
            tail.next = newNode;
            tail = newNode;
        }
    }

    public int dequeue() {
        if (head == null) {
            throw new RuntimeException("Queue is empty");
        }

        int value = head.value;
        head = head.next;
        if (head == null) {
            tail = null;
        }
        return value;
    }
}

class Stack<T> {
    private List<T> elements = new ArrayList<>();

    public void push(T element) {
        elements.add(element);
    }

    public T pop() {
        if (elements.isEmpty()) {
            throw new RuntimeException("Stack is empty");
        }
        return elements.remove(elements.size() -1);
    }

    public T peek() {
        if (elements.isEmpty()) {
            throw new RuntimeException("Stack is empty");
        }
        return elements.get(elements.size() -1);
    }
}

class TreeNode {
    private String name;
    private List<TreeNode> children;

    // ... 其他代码
}

class FileSystem {
    private TreeNode root;

    // ... 其他代码
}

public static void quickSort(int[] arr) {
    if (arr == null || arr.length <= 1) {
        return;
    }

    int pivot = arr[0];
    int leftIndex = 0;
    int rightIndex = arr.length - 1;

    while (leftIndex < rightIndex) {
        while (arr[rightIndex] >= pivot && rightIndex > leftIndex) {
            rightIndex--;
        }
        arr[leftIndex] = arr[rightIndex];

        while (arr[leftIndex] <= pivot && rightIndex > leftIndex) {
            leftIndex++;
        }
        arr[rightIndex] = arr[leftIndex];
    }
    arr[leftIndex] = pivot;

    quickSort(arr, 0, leftIndex - 1);
    quickSort(arr, leftIndex + 1, arr.length - 1);
}

public static int binarySearch(int[] arr, int target) {
    int left = 0;
    int right = arr.length - 1;

    while (left <= right) {
        int mid = (left + right) / 2;

        if (arr[mid] == target) {
            return mid;
        } else if (arr[mid] < target) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }
    return -1;
}