数据结构之树（Java 实现版）

实现功能：

　　1.实现了树的构建；

　　2.实现了树的前序递归遍历、后序递归遍历、中序递归遍历；

class BinaryTreeNode{
        int data;
        BinaryTreeNode leftNode = null, rightNode = null;
        
        public void setBinaryTreeNode(int data) {
            this.data = data;
        }
        public void setLeftNode(BinaryTreeNode leftNode) {
            this.leftNode = leftNode;
        }
        public void setRightNode(BinaryTreeNode rightNode) {
            this.rightNode = rightNode;
        }
    }

class BinaryTree{
    BinaryTreeNode[] btn;
    BinaryTreeNode rooNode;
    int NodeSize;
    
    public BinaryTree(int[] arrayNode) {
        NodeSize = arrayNode.length;
        btn = new BinaryTreeNode[NodeSize];
        
        //把arrayNode元素转化为节点
        for(int i = 0; i < NodeSize; i++){
            btn[i] = new BinaryTreeNode();
            btn[i].setBinaryTreeNode(arrayNode[i]);
            if(i == 0){
                rooNode = btn[i];
            }
        }
        //把二叉树的左右子树节点补全
        for(int j = 0; j <= (NodeSize - 2)/2; j++){
            btn[j].setLeftNode(btn[2*j + 1]);
            btn[j].setRightNode(btn[2*j + 2]);
        }
    }
    //递归方法前序遍历
    void preOrder(BinaryTreeNode btn){
        BinaryTreeNode root = btn;
        if(root != null){
            printNode(root);
            inOrder(root.leftNode);
            inOrder(root.rightNode);
        }
    }
    //递归方法中序遍历
    void inOrder(BinaryTreeNode btn){
        BinaryTreeNode root = btn;
        
        if(root != null){
            inOrder(root.leftNode);
            printNode(root);
            inOrder(root.rightNode);
        }
    }
    //递归方法后序遍历
    void postOrder(BinaryTreeNode btn){
        BinaryTreeNode root = btn;
        
        if(root != null){
            postOrder(root.leftNode);
            postOrder(root.rightNode);
            printNode(root);
        }
    }
    //打印节点信息
    static void printNode(BinaryTreeNode btn){
        int a = btn.data;
        System.out.println(a);
    }
}

public class Tree {
    public static void main(String[] args) {
        int[] arrayNode = new int[]{1,2,3,4,5,6,7,8,9};
        BinaryTree bt = new BinaryTree(arrayNode);
        System.out.println("inOrder:");
        bt.inOrder(bt.rooNode);
        System.out.println("preOrder:");
        bt.preOrder(bt.rooNode);
        System.out.println("postOrder:");
        bt.postOrder(bt.rooNode);
    }
}