二叉树

      树是这样的数据结构，可以像链表那样快速地插入和删除，也可以像有序数组那样快速地查询；二叉树，只有两个字节点。
    

class Node
{

    public final int    iData;
    public final double fData;
    public Node         leftChild;
    public Node         rightChild;

    public Node(int id, double fd)
    {
        iData = id;
        fData = fd;
    }

    public void displayNode()
    {
        System.out.println(iData + fData);
    }
}

class Tree
{

    public Node root;

    /**
     * 左孩子小于结点，右孩子大于结点
     * 
     * @param id
     * @param dd
     */
    public void insert(int id, double dd)
    {
        Node newNode = new Node(id, dd);
        if(root == null)
            root = newNode;
        else
        {
            Node parent;
            Node current = root;
            while (true)
            {
                parent = current;
                if(current.iData > id)
                {
                    current = current.leftChild;
                    if(current == null)
                    {
                        parent.leftChild = newNode;
                        return;
                    }
                }
                else
                {
                    current = current.rightChild;
                    if(current == null)
                    {
                        parent.rightChild = newNode;
                        return;
                    }
                }
            }

        }
    }

    public Tree()
    {
        root = null;
    }

    public boolean delete(int key)
    {
        Node current = root;
        Node parent = root;
        boolean isLeftChild = true;
        while (current.iData != key)
        {
            parent = current;
            if(current.iData > key)
            {
                isLeftChild = true;
                current = current.leftChild;
            }
            else
            {
                isLeftChild = false;
                current = current.rightChild;
            }
            if(current == null)
                return false;
        }
        // 分三种可能，无子结点，有一个子结点，有两个子节点
        delWithNode(current, parent, isLeftChild);
        return true;
    }

    public void delWithNode(Node current, Node parent, boolean isLeftChild)
    {
        if(current.leftChild == null && current.rightChild == null)
        {
            if(current == root)
                root = null;
            else
                if(isLeftChild)
                    parent.leftChild = null;
                else
                    parent.rightChild = null;
        }
        else
            if(current.leftChild != null && current.rightChild == null)
            {
                if(current == root)
                    root = current.leftChild;
                else
                    if(isLeftChild)
                        parent.leftChild = current.leftChild;
                    else
                        parent.rightChild = current.leftChild;
            }
            else
                if(current.rightChild != null && current.leftChild == null)
                {
                    if(current == root)
                        root = current.rightChild;
                    else
                        if(isLeftChild)
                            parent.leftChild = current.rightChild;
                        else
                            parent.rightChild = current.rightChild;
                }
                else
                {
                    Node successNode = getSuccessor(current);
                    if(current == root)
                        root = successNode;
                    else
                        if(isLeftChild)
                            parent.leftChild = successNode;
                        else
                            parent.rightChild = successNode;
                    successNode.leftChild = current.leftChild; // 将要删除的结点的左子树传给新的节点
                }
    }

    /**
     * 当要删除的结点有左右两个子结点时获取要替换的结点
     * 
     * @param delNode
     * @return
     */
    private Node getSuccessor(Node delNode)
    {
        Node successNode = delNode;
        Node successParent = delNode;
        Node current = successNode.rightChild;
        while (current != null)
        { //查找右子树的最小值，即右子数的最左节点
            successParent = successNode;
            successNode = current;
            current = current.leftChild;
        }
        if(successNode != delNode.rightChild)
        { // 如果要替换的结点不是其右结点，处理该结点右边的结点
            successParent.leftChild = successNode.rightChild;
            successNode.rightChild = delNode.rightChild;
        }
        return successNode;
    }

    /**
     * 前序遍历:访问根；按前序遍历左子树；按前序遍历右子树
     * 
     * @param localNode
     */
    public void preOrder(Node localNode)
    {
        if(localNode != null)
        {
            System.out.print(localNode.iData + " ");
            preOrder(localNode.leftChild);
            preOrder(localNode.rightChild);
        }
    }

    /**
     * 中序遍历:按中序遍历左子树；访问根；按中序遍历右子树
     * 
     * @param localNode
     */
    public void inOrder(Node localNode)
    {
        if(localNode != null)
        {
            inOrder(localNode.leftChild);
            System.out.print(localNode.iData + " ");
            inOrder(localNode.rightChild);
        }
    }

    /**
     * 后序遍历:按后序遍历左子树；按后序遍历右子树；访问根
     * 
     * @param localNode
     */
    public void postOrder(Node localNode)
    {
        if(localNode != null)
        {
            postOrder(localNode.leftChild);
            postOrder(localNode.rightChild);
            System.out.print(localNode.iData + " ");
        }
    }
}

注：以上代码均出自java数据结构与算法第二版