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树的汇�?�?

Sha Jiang — Thu, 25 Jun 2009 23:11:00 GMT

树的汇�?/span>

�l�上�ơ浅谈了树的遍历之后�Q�这�ơ再��谈一下树的汇怅R�?wbr>此处的汇��L��指将树中某个节点的数据按指定的规则汇集到它的父节点中�?wbr>例如�Q�可以将树节点中的数值篏加到它的父节点中�?wbr>仍如树的遍历一文，我将使用两种��单的��法�Q�递归与和�q�代�Q?wbr>来实现这一功能�?2009.08.09最后更�?

1. 树节�?/span>
仍然沿用树的遍历一文中的TreeNode/GenericTreeNode�Q��ؓ便于阅读�Q?wbr>��GenericTreeNode中的若干关键属性展�C�如下，

2. 递归�?/span>
仍然先从最��单的递归法开始，

public static Double recursiveGatherValue(GenericTreeNode<Double> node) {
    Double sumValue = null;
    if (node.isLeaf()) {
        return node.getUserObject();
    } else {
        sumValue = node.getUserObject();
        List<GenericTreeNode<Double>> children = node.getChildren();
        for (int i = 0, size = children.size(); i < size; i++) {
            Double bufGatherValue = recursiveGatherValue(children.get(i));
            sumValue += bufGatherValue;
        }
    }

    node.setUserObject(sumValue);
    return sumValue;
}

递归法还是一如既往的简单易懂。与递归遍历树相比，递归汇��L��的程序基本上没大的变化，我就不赘�q�C��...

3. �q�代�?/span>
与�P代遍历树相比�Q��P代汇��L��的程序有一些明昄��变化�?wbr>当初在思考�P代法�Ӟ��有个问题一直困�l�着我：如何��下�U�节点的��D��l�它的父节点�Q��ƈ且父节点的��D��不断的进行篏加。在JavaWorld@TW中提��个问题之�?wbr>�Q�很快就得到�?a >清晰的解�{?/a>(真的很感谢社区里的大大们)�?wbr>毫无疑问�Q�用�q�代法遍历一��|��旉��要��用一个栈�Q�但同时�Q��ؓ了维护节点与汇��d��g��间的关系�Q?wbr>�q�需要另一个栈�q�行辅助。具体程序如下所�C�，

public static void iterativeGatherValue(GenericTreeNode<Double> node) {
    Stack<NodeValueTuple<Double>> nodeValueStack = new Stack<NodeValueTuple<Double>>();
    Stack<GenericTreeNode<Double>> nodeStack = new Stack<GenericTreeNode<Double>>();

    nodeStack.push(node);
    Double sumValue = new Double(0.0D);
    while (!nodeStack.isEmpty()) {
        GenericTreeNode<Double> bufNode = nodeStack.pop();
        if (bufNode == null) {
            NodeValueTuple<Double> bufNodeValueTuple = nodeValueStack.pop();
        bufNodeValueTuple.node.setUserObject(sumValue);

        sumValue += bufNodeValueTuple.value;
        } else if (bufNode.isLeaf()) {
            sumValue += bufNode.getUserObject();
        } else {
            nodeValueStack.add(new NodeValueTuple<Double>(bufNode, sumValue));

            sumValue = new Double(0.0D);
            nodeStack.push(null);
            nodeStack.addAll(bufNode.getChildren());
        }
    }
}

在遍历树的过�E�中�Q�会��某节点N与它的汇��d��g��同置入一个栈(nodeValueStack)中，当节点N有子节点�Ӟ��则将它的子节点及其汇��d��g��|�入栈中�Q�节点N与它的子节点之间使用一个NULL��D��行分隔；如果节点N是叶节点则篏加汇��d��|��如果节点N为NULL�Q?wbr>则表�C�子节点们的汇��d��l�束�?br /> NodeValueTuple是一个二元组�Q?wbr>用于�l�护节点与它的汇��d��g��间的关系�Q�代码如下所�C�，

public class NodeValueTuple<V> {

    public final GenericTreeNode<V> node;
    public final V value;

    public NodeValueTuple(GenericTreeNode<V> node, V value) {
        this.node = node;
        this.value = value;
    }
}

在上�q�的汇��M��Q�均只篏加了叶节点中的数��|��而不��分枝节点和根节�Ҏ��w�所拥有的数倹{�?wbr>如果要篏加这些节�Ҏ��w�的数��|��应该如何做呢�Q?wbr>大家自己做做看吧�Q�肯定非常简�?^_^

4. ��结
树的汇总肯定是一个十分常见的应用�Q�除了汇��L��据之外，我们�q�可以汇集节点中的对象，如汇��L��载在节点上的集合对象中的元素�Q?wbr>使得父节点能够拥有所有子节点所拥有的元素。上�q�方法的效率应该不算低，主要是因为所有的树节点只需要访问一�ơ�?br />

Sha Jiang 2009-06-26 07:11 发表评论

树的遍历(�?

Sha Jiang — Wed, 01 Apr 2009 12:40:00 GMT

树的遍历

之前的工作都没有接触到树�Q�也��很��研�I�它。幸�q�地的是�Q�在目前的工作中多次遇到树型�l�构的数据，那么讉K��树节点中的数据就是必然的了，而且�q�需要按照指定规则对节点中的数据�q�行额外处理。经�q�学习之后，对与树相关的基本��法有了一些认知，��p��划写几篇��文。其实这��L��文章早已是汗牛充栋，而我只是把它当作我的学习�ȝ��|�了�Q�以加深记忆与理解，如能对其他朋友有所助益�Q�则更感愉悦�?:-) (2009.04.03最后更�?

�q�次先从最基础的开�?-树的遍历。本文��用了两种极常用的�Ҏ��来遍历树中的所有节�?-递归�Q��P代，但它们实现的都是深度优先(Depth-First)��法�?br />
1. 树节点与数据
先定义树节点及数�?用户对象)�Q��ƈ创徏��试用的数据�?br /> TreeNode是树节点的定义�?br />

/**
* 树节点的定义�?br /> */
public interface TreeNode {

    /**
     * 获取指定下标处的子节炏V�?br />      *
     * @param index
     *            下标�?br />      * @return 子节炏V�?br />      */
    public TreeNode getChildAt(int index);

    /**
     * �q�回指定子节点的下标�?br />      *
     * @param index
     *            下标�?br />      * @return 子节炏V�?br />      */
    public int getChildIndex(TreeNode index);

    /**
     * 获取子节点的数量�?br />      *
     * @return 子节点的数量�?br />      */
    public int getChildCount();

    /**
     * �q�回父节炏V�?br />      *
     * @return 父节炏V�?br />      */
    public TreeNode getParent();

    /**
     * 讄��父节炏V��注�Q�此处不需要改变父节点中的子节点元素�?br />      *
     * @param parent
     *            父节炏V�?br />      */
    public void setParent(TreeNode parent);

    /**
     * 获取所有的子节炏V�?br />      *
     * @return 子节点的集合�?br />      */
    public List getChildren();

    /**
     * 是否为叶节点�?br />      *
     * @return 是叶节点�Q�返回true�Q�否则，�q�回false�?br />      */
    public boolean isLeaf();
}

GenericTreeNode是一个通用的树节点实现�?br />

public class GenericTreeNode<T> implements TreeNode {

    private T userObject = null;

    private TreeNode parent = null;

    private List<GenericTreeNode<T>> children = new ArrayList<GenericTreeNode<T>>();

    public GenericTreeNode(T userObject) {
        this.userObject = userObject;
    }

    public GenericTreeNode() {
        this(null);
    }

    /**
     * ��d��子节炏V�?br />      *
     * @param child
     */
    public void addChild(GenericTreeNode<T> child) {
        children.add(child);
        child.setParent(this);
    }

    /**
     * 删除指定的子节点�?br />      *
     * @param child
     *            子节炏V�?br />      */
    public void removeChild(TreeNode child) {
        removeChildAt(getChildIndex(child));
    }

    /**
     * 删除指定下标处的子节炏V�?br />      *
     * @param index
     *            下标�?br />      */
    public void removeChildAt(int index) {
        TreeNode child = getChildAt(index);
        children.remove(index);
        child.setParent(null);
    }

    public TreeNode getChildAt(int index) {
        return children.get(index);
    }

    public int getChildCount() {
        return children.size();
    }

    public int getChildIndex(TreeNode child) {
        return children.indexOf(child);
    }

    public List<GenericTreeNode<T>> getChildren() {
        return Collections.unmodifiableList(children);
    }

    public void setParent(TreeNode parent) {
        this.parent = parent;
    }

    public TreeNode getParent() {
        return parent;
    }

    /**
     * 是否为根节点�?br />      *
     * @return 是根节点�Q�返回true�Q�否则，�q�回false�?br />      */
    public boolean isRoot() {
        return getParent() == null;
    }

    public boolean isLeaf() {
        return getChildCount() == 0;
    }

    /**
     * 判断指定的节�Ҏ��否�ؓ当前节点的子节点�?br />      *
     * @param node
     *            节点�?br />      * @return 是当前节点的子节点，�q�回true�Q�否则，�q�回false�?br />      */
    public boolean isChild(TreeNode node) {
        boolean result;
        if (node == null) {
            result = false;
        } else {
            if (getChildCount() == 0) {
                result = false;
            } else {
                result = (node.getParent() == this);
            }
        }

        return result;
    }

    public T getUserObject() {
        return userObject;
    }

    public void setUserObject(T userObject) {
        this.userObject = userObject;
    }

    @Override
    public String toString() {
        return userObject == null ? "" : userObject.toString();
    }
}

UserObject是节点上的用户对象，相当于是数据�?br />

public class UserObject {

    private String name = null;

    private Integer value = Integer.valueOf(0);

    public UserObject() {

    }

    public UserObject(String code, Integer value) {
        this.name = code;
        this.value = value;
    }

    public String getName() {
        return name;
    }

    public void setName(String code) {
        this.name = code;
    }

    public Integer getValue() {
        return value;
    }

    public void setValue(Integer value) {
        this.value = value;
    }

    @Override
    public String toString() {
        StringBuilder result = new StringBuilder();
        result.append("[name=").append(name).append(", value=").append(value).append("]");
        return result.toString();
    }
}

TreeUtils是用于创建树的工��L��?br />

public class TreeUtils {

    public static GenericTreeNode<UserObject> buildTree() {
        GenericTreeNode<UserObject> root = new GenericTreeNode<UserObject>();
        root.setUserObject(new UserObject("ROOT", Integer.valueOf(0)));

        GenericTreeNode<UserObject> node1 = new GenericTreeNode<UserObject>();
        node1.setUserObject(new UserObject("1", Integer.valueOf(0)));
        GenericTreeNode<UserObject> node2 = new GenericTreeNode<UserObject>();
        node2.setUserObject(new UserObject("2", Integer.valueOf(0)));
        GenericTreeNode<UserObject> node3 = new GenericTreeNode<UserObject>();
        node3.setUserObject(new UserObject("3", Integer.valueOf(5)));

        root.addChild(node1);
        root.addChild(node2);
        root.addChild(node3);

        GenericTreeNode<UserObject> node11 = new GenericTreeNode<UserObject>();
        node11.setUserObject(new UserObject("11", Integer.valueOf(0)));
        GenericTreeNode<UserObject> node21 = new GenericTreeNode<UserObject>();
        node21.setUserObject(new UserObject("21", Integer.valueOf(0)));

        node1.addChild(node11);
        node2.addChild(node21);

        GenericTreeNode<UserObject> node111 = new GenericTreeNode<UserObject>();
        node111.setUserObject(new UserObject("111", Integer.valueOf(3)));
        GenericTreeNode<UserObject> node112 = new GenericTreeNode<UserObject>();
        node112.setUserObject(new UserObject("112", Integer.valueOf(9)));
        GenericTreeNode<UserObject> node211 = new GenericTreeNode<UserObject>();
        node211.setUserObject(new UserObject("211", Integer.valueOf(6)));
        GenericTreeNode<UserObject> node212 = new GenericTreeNode<UserObject>();
        node212.setUserObject(new UserObject("212", Integer.valueOf(3)));

        node11.addChild(node111);
        node11.addChild(node112);
        node21.addChild(node211);
        node21.addChild(node212);

        return root;
    }
}

2. 递归�?/strong>
使用递归法的最大好处就�?-��单，但一般地�Q�我们都认�ؓ递归的效率不高�?br />
private static void recursiveTravel(GenericTreeNode<UserObject> node) {
    travelNode(node); // 讉K��节点�Q�仅仅只是打印该节点�|�了�?/span>
    List<GenericTreeNode<UserObject>> children = node.getChildren();
    for (int i = 0; i < children.size(); i++) {
        recursiveTravel(children.get(i)); // 递归地访问当前节点的所有子节点�?/span>
    }
}
大家肯定知道�Q�系�l�在执行递归�Ҏ��(对于其它�Ҏ��也是如此)时是使用�q�行时栈。对�Ҏ��的每一�ơ调用，在栈中都会创��Z��份此�ơ调用的�z�d��记录--包括�Ҏ��的参敎ͼ�局部变量，�q�回地址�Q�动态链接库�Q�返回值等�?br /> 既然�pȝ��能够隐式��C��用栈��L��行递归�Ҏ��Q�那么我们就可以昑ּ��C��用栈来执行上�q�递归�E�序�Q�这也是��递归�E�序转化��P代程序的常用思想。下面的iterativeTravel�Ҏ��p��用了�q�一思想�?br />
3. �q�代�?/strong>

private static void iterativeTravel(GenericTreeNode<UserObject> node) {
    Stack<GenericTreeNode<UserObject>> nodes = new Stack<GenericTreeNode<UserObject>>();

    nodes.push(node); // ��当前节点压入栈中�?/span>
    while (!nodes.isEmpty()) {
        GenericTreeNode<UserObject> bufNode = nodes.pop(); // 从栈中取��Z��个节炏V�?/span>
        travelNode(bufNode); // 讉K��节点�?/span>
        if (!bufNode.isLeaf()) { // 如果该节点�ؓ分枝节点�Q�则��它的子节点全部加入栈中�?/span>
            nodes.addAll(bufNode.getChildren());
        }
    }
}
与递归法相比，�q�代法的代码略多了几行，但仍然很��单�?br />
4. ��结
�׃��上述两种�Ҏ��?隐式或显式地)使用了运行栈�Q�所以此处的�q�代法�ƈ不能提高整个�E�序的效率。相反地�Q�由于在应用�E�序中显式地使用�?java.util.Stack)�Q�iterativeTravel�Ҏ��的效率可能反而更低。但iterativeTravel的最大好处是�Q�能够有效地避免�q�行时栈溢出(java.lang.StackOverflowError)�?br /> 如果树的层次不太深，每层的子节点��C��太多�Q�那么��用递归法应该是没有问题的。毕竟，��z�地�E�序会提供更多的好处�?br />

Sha Jiang 2009-04-01 20:40 发表评论

判定一个点是否在三角�Ş�?�?

Sha Jiang — Thu, 24 Jul 2008 09:02:00 GMT

判定一个点是否在三角�Ş�?/span>

如何判定一个点P是否存在于指定的三角形ABC内，�q�肯定是一个简单的问题�Q�本文仅用一个图形界面程序展�C�Z��该问题，有兴��的朋友可以看看�?2008.07.24最后更�?

在此处��用一�U�常见且��便的�Ҏ��Q?strong>如果三角形PAB�Q�PAC和PBC的面�U�之和与三角形ABC的面�U�相�{�，卛_��判定点P在三角�ŞABC�?包括在三条边�?�?br /> 可知�Q�该�Ҏ��的关键在于如何计��三角�Ş的面�U�。幸�q�地是，当知道三角�Ş��点(A�Q�B和C)的坐�?(Ax, Ay)�Q?Bx, By)�?Cx, Cy))之后�Q�即可计��出光��U�：

S = |(Ax * By + Bx * Cy + Cx * Zy - Ay * Bx - By * Cx - Cy * Ax) / 2|

关键的代码如下，

// ��q��定的三个��点的坐标，计算三角形面�U��?br /> // Point(java.awt.Point)代表点的坐标�?/span>
private static double triangleArea(Point pos1, Point pos2, Point pos3) {
    double result = Math.abs((pos1.x * pos2.y + pos2.x * pos3.y + pos3.x * pos1.y
            - pos2.x * pos1.y - pos3.x * pos2.y - pos1.x * pos3.y) / 2.0D);
    return result;
}

// 判断点pos是否在指定的三角形内�?/span>
private static boolean inTriangle(Point pos, Point posA, Point posB,
        Point posC) {
    double triangleArea = triangleArea(posA, posB, posC);
    double area = triangleArea(pos, posA, posB);
    area += triangleArea(pos, posA, posC);
    area += triangleArea(pos, posB, posC);
    double epsilon = 0.0001;  // �׃��点数的计算存在着误差�Q�故指定一个��够小的数�Q�用于判定两个面�U�是�?�q�似)相等�?/span>
    if (Math.abs(triangleArea - area) < epsilon) {
        return true;
    }
    return false;
}

执行该应用程序，用鼠标在其中点击三次�Q�即可绘制一个三角�Ş�Q�如下组图所�C�：

然后仅需�U�d��鼠标�Q�就会出��C��个空心圆圈。如果圆圈的中心在三角内(包含在三条边�?�Q�则圆圈昄��为红�Ԍ��否则�Q�显�C�Zؓ蓝色。如下组图所�C�：

完整代码如下�Q?br />
public class CanvasPanel extends JPanel {

    private static final long serialVersionUID = -6665936180725885346L;

    private Point firstPoint = null;

    private Point secondPoint = null;

    private Point thirdPoint = null;

    public CanvasPanel() {
        setBackground(Color.WHITE);
        addMouseListener(mouseAdapter);
        addMouseMotionListener(mouseAdapter);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        drawTriangel(g);
    }

    private void drawTriangel(Graphics g) {
        if (firstPoint != null && secondPoint != null) {
            g.drawLine(firstPoint.x, firstPoint.y, secondPoint.x, secondPoint.y);
            if (thirdPoint != null) {
                g.drawLine(firstPoint.x, firstPoint.y, thirdPoint.x, thirdPoint.y);
                g.drawLine(secondPoint.x, secondPoint.y, thirdPoint.x, thirdPoint.y);
            }
        }
    }

    private static boolean inTriangle(Point pos, Point posA, Point posB,
            Point posC) {
        double triangeArea = triangleArea(posA, posB, posC);
        double area = triangleArea(pos, posA, posB);
        area += triangleArea(pos, posA, posC);
        area += triangleArea(pos, posB, posC);
        double epsilon = 0.0001;
        if (Math.abs(triangeArea - area) < epsilon) {
            return true;
        }
        return false;
    }

    private static double triangleArea(Point pos1, Point pos2, Point pos3) {
        double result = Math.abs((pos1.x * pos2.y + pos2.x * pos3.y + pos3.x * pos1.y
                            - pos2.x * pos1.y - pos3.x * pos2.y - pos1.x * pos3.y) / 2.0D);
        return result;
    }

    private MouseInputAdapter mouseAdapter = new MouseInputAdapter() {

        public void mouseReleased(MouseEvent e) {
            Point pos = e.getPoint();
            if (firstPoint == null) {
                firstPoint = pos;
            } else if (secondPoint == null) {
                secondPoint = pos;
                Graphics g = CanvasPanel.this.getGraphics();
                CanvasPanel.this.paintComponent(g);
                g.drawLine(firstPoint.x, firstPoint.y, secondPoint.x, secondPoint.y);
            } else if (thirdPoint == null) {
                thirdPoint = pos;
                Graphics g = CanvasPanel.this.getGraphics();
                CanvasPanel.this.paintComponent(g);
                g.drawLine(firstPoint.x, firstPoint.y, secondPoint.x, secondPoint.y);
                g.drawLine(firstPoint.x, firstPoint.y, thirdPoint.x, thirdPoint.y);
                g.drawLine(secondPoint.x, secondPoint.y, thirdPoint.x, thirdPoint.y);
            }
        }

        public void mouseMoved(MouseEvent e) {
            Point pos = e.getPoint();
            Graphics2D g2 = (Graphics2D) CanvasPanel.this.getGraphics();
            CanvasPanel.this.paintComponent(g2);
            if (firstPoint != null && secondPoint == null) {
                g2.drawLine(firstPoint.x, firstPoint.y, pos.x, pos.y);
            } else if (firstPoint != null && secondPoint != null && thirdPoint == null) {
                g2.drawLine(firstPoint.x, firstPoint.y, pos.x, pos.y);
                g2.drawLine(secondPoint.x, secondPoint.y, pos.x, pos.y);
            } else if (firstPoint != null && secondPoint != null && thirdPoint != null) {
                if (inTriangle(pos, firstPoint, secondPoint, thirdPoint)) {
                    g2.setColor(Color.RED);
                } else {
                    g2.setColor(Color.BLUE);
                }
                int radius = 4;
                g2.drawOval(pos.x - radius, pos.y - radius, radius * 2, radius * 2);
            }
        }
    };
}

public class Triangle extends JFrame {

    private static final long serialVersionUID = 1L;

    private CanvasPanel mainPanel = null;

    public Triangle() {
        setTitle("Triangle");
        setSize(new Dimension(300, 200));
        setResizable(false);

        init();

        Container container = getContentPane();
        container.add(mainPanel);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }

    private void init() {
        mainPanel = new CanvasPanel();
    }

    public static void main(String[] args) {
        new Triangle();
    }
}

Sha Jiang 2008-07-24 17:02 发表评论