二叉树的基本操作

TreeNode 类

class TreeNode {        int data;        TreeNode leftNode;        TreeNode rightNode;        public TreeNode() {        }        public TreeNode(int data) {            this.data = data;        }}

1. 前序遍历（中左右）

    /**     * 前序遍历     *      * @param root     */    public static void preOrder(TreeNode root) {        if (root == null)            return;        System.out.print(root.data + " ");        preOrder(root.leftNode);        preOrder(root.rightNode);    }

2. 中序遍历（左中右）

     /**     * 中序遍历     *      * @param root     */    public static void inOrder(TreeNode root) {        if (root == null)            return;        inOrder(root.leftNode);        System.out.print(root.data + " ");        inOrder(root.rightNode);    }

3. 后序遍历（左右中）

     /**     * 后序遍历     *      * @param root     */    public static void postOrder(TreeNode root) {        if (root == null)            return;        postOrder(root.leftNode);        postOrder(root.rightNode);        System.out.print(root.data + " ");    }

4. 查找节点

    /**     * 查找节点     *      * @param data     * @param root     * @return     */    public static TreeNode findNode(int data, TreeNode root) {        if (root == null)            return null;        TreeNode current = root;        while (current.data != data) {            if (data < current.data) {                current = current.leftNode;            } else {                current = current.rightNode;            }            if (current == null)                return null;        }        return current;    }

5. 插入节点

     /**     * 插入节点     *      * @param newNode     * @param root     */    public static void insertNode(TreeNode newNode, TreeNode root) {        if (newNode == null)            return;        if (root == null) {            root = newNode;            return;        }        TreeNode current = root;        while (true) {            if (newNode.data < current.data) {                if (current.leftNode == null) {                    current.leftNode = newNode;                    return;                }                current = current.leftNode;            } else {                if (current.rightNode == null) {                    current.rightNode = newNode;                    return;                }                current = current.rightNode;            }        }    }

6. 删除节点

    /**     * 删除节点     * @param data     * @param root     * @return     */    public static boolean deleteNode(int data, TreeNode root) {        if (root == null)            return false;        TreeNode current = root;        TreeNode parent = root;        boolean isLeftChild = false;        while (data != current.data) {            parent = current;            if (data < current.data) {                isLeftChild = true;                current = current.leftNode;            } else {                isLeftChild = false;                current = current.rightNode;            }            if (current == null)                return false;        }        if (current.leftNode == null && current.rightNode == null) {            if (current == root) {                root = null;                return true;            } else if (isLeftChild) {                parent.leftNode = null;            } else {                parent.rightNode = null;            }        } else if (current.leftNode == null) {            if (current == root) {                root = root.rightNode;                return true;            } else if (isLeftChild) {                parent.leftNode = current.rightNode;            } else {                parent.rightNode = current.rightNode;            }        } else if (current.rightNode == null) {            if (current == root) {                root = root.leftNode;            } else if (isLeftChild) {                parent.leftNode = current.leftNode;            } else {                parent.rightNode = current.rightNode;            }        } else {            TreeNode successor = getSuccessor(current);            if (current == root) {                root = successor;            }else if(isLeftChild){                parent.leftNode = successor;            }else{                parent.rightNode = successor;            }                   successor.leftNode = current.leftNode;        }        return true;    }    /**     * 获取后继节点     * @param delNode     * @return     */    private static TreeNode getSuccessor(TreeNode delNode) {        TreeNode successorParent = delNode;        TreeNode successor = delNode;        TreeNode current = delNode.rightNode;        while (current != null) {            successorParent = successor ;            successor = current;            current = current.leftNode;        }        if(successor != delNode.rightNode){            successorParent.leftNode = successor.rightNode;            successor.rightNode = delNode.rightNode;        }        return successor;    }