构造排序二叉树，并按行从左到右输出

import java.util.LinkedList;import java.util.Queue;public class Main {    class BinaryNode {        int val;        BinaryNode left;        BinaryNode right;        public BinaryNode(int val) {            this.val = val;        }    }//BinaryNode    private BinaryNode root;//根节点,这个属性很重要    private void buildOrderTree(int[] vals) {        for (int i = 0; i < vals.length; i++) {            insert(vals[i]);        }    }//build    private void insert(int val) {        root = insert(root, val);    }//insert    private BinaryNode insert(BinaryNode root, int val) {        if (root == null)            return new BinaryNode(val);        if (val <= root.val)            root.left = insert(root.left, val);//把该结点赋值给root结点的左孩子        else                                   //把该结点赋值给root结点的右孩子            root.right = insert(root.right, val);//这里是递归，2在栈中没弹出来，4压入栈，4弹出栈后，栈中还有2，返回2        return root;    }//insert    public void printTreeLineByLine(BinaryNode root) {        Queue<BinaryNode> queue = new LinkedList<BinaryNode>();//把待打印的结点放在队列中        BinaryNode curNode;        queue.offer(root);        int curNum = 1;//当前行未打印的节点数        int next = 0;//下一行待打印的节点数        while (!queue.isEmpty()) {            curNode = queue.poll();            System.out.print(curNode.val + " ");            curNum--;            if (curNode.left != null) {                queue.offer(curNode.left);                next++;            }            if (curNode.right != null) {                queue.offer(curNode.right);                next++;            }            if (curNum == 0) {                curNum = next;                next = 0;                System.out.println();//换行            }        }//while    }//printTreeLineByLine    public static void main(String[] args) {        Main bst = new Main();//        int[] arr = {2, 4, 5, 1, 3,6,7,8,9,10,12,13,14,15,16,17,18};        int[] arr = {2, 4, 5, 1, 3, 6, 7, 8};//        int[] arr = {2, 4, 5, 1, 3};        bst.buildOrderTree(arr);        bst.printTreeLineByLine(bst.root);//用到了root属性    }}//2//1 4//3 5//6//7//8

参考：http://www.cnblogs.com/hapjin/p/5738354.html