P137、面试题23：从上往下打印二叉树

题目：从上往下打印出二叉树的每个结点，同一层的结点按照从左到右的顺序打印。例如输入如图的二叉树，则依次打印出8,6,10,5,7,9,11.(其实是按层遍历)
二叉树结点的定义如下：
struct BinaryTreeNode{
       int     m_nValue;
       BinaryTreeNode*     m_pLeft;
       BinaryTreeNode*     m_pRight;
}

代码实现：

package com.yyq;

import java.util.LinkedList;
import java.util.Queue;

/**
 * Created by Administrator on 2015/9/16.
 */
public class PrintFromTopToBottom {
    public static void printFromTopToBottom(BinaryTreeNode pTreeRoot){
        if (pTreeRoot == null)
            return;
        Queue<BinaryTreeNode> queue = new LinkedList<BinaryTreeNode>();
        queue.offer(pTreeRoot);
        while (queue.size() > 0){
            BinaryTreeNode pNode = queue.poll();
            System.out.print(pNode.getM_nValue() + "\t");
            if (pNode.getM_pLeft() != null){
                queue.offer(pNode.getM_pLeft());
            }
            if (pNode.getM_pRight() != null){
                queue.offer(pNode.getM_pRight());
            }
        }
    }
    // ====================测试代码====================
    public static void Test(String testName, BinaryTreeNode pRoot){
        if (testName != null)
            System.out.println(testName + " Begin:");
        printFromTopToBottom(pRoot);
        System.out.println();
    }
// 测试完全二叉树：除了叶子节点，其他节点都有两个子节点
//            8
//        6      10
//       5 7    9  11
    public static void Test1() {
        System.out.println("\n=====Test1 starts:=====");
        BinaryTreeNode pNode8 = new BinaryTreeNode(8);
        BinaryTreeNode pNode6 = new BinaryTreeNode(6);
        BinaryTreeNode pNode10 = new BinaryTreeNode(10);
        BinaryTreeNode pNode5 = new BinaryTreeNode(5);
        BinaryTreeNode pNode7 = new BinaryTreeNode(7);
        BinaryTreeNode pNode9 = new BinaryTreeNode(9);
        BinaryTreeNode pNode11 = new BinaryTreeNode(11);

        pNode8.connectTreeNodes(pNode6, pNode10);
        pNode6.connectTreeNodes(pNode5, pNode7);
        pNode10.connectTreeNodes(pNode9, pNode11);

        Test("Test1",pNode8);
        pNode8 = null;
    }

    // 测试二叉树：出叶子结点之外，左右的结点都有且只有一个左子结点
//            8
//          7
//        6
//      5
//
    public static void Test2() {
        System.out.println("\n=====Test2 starts:=====");
        BinaryTreeNode pNode8 = new BinaryTreeNode(8);
        BinaryTreeNode pNode7 = new BinaryTreeNode(7);
        BinaryTreeNode pNode6 = new BinaryTreeNode(6);
        BinaryTreeNode pNode5 = new BinaryTreeNode(5);
        BinaryTreeNode pNode4 = new BinaryTreeNode(4);

        pNode8.connectTreeNodes(pNode7, null);
        pNode7.connectTreeNodes(pNode6, null);
        pNode6.connectTreeNodes(pNode5, null);
        pNode5.connectTreeNodes(pNode4, null);

        Test("Test2",pNode8);
        pNode8 = null;
    }

    // 测试二叉树：出叶子结点之外，左右的结点都有且只有一个右子结点
//            8
//             7
//              6
//               5
//                4
    public static void Test3() {
        System.out.println("\n=====Test3 starts:=====");
        BinaryTreeNode pNode8 = new BinaryTreeNode(8);
        BinaryTreeNode pNode7 = new BinaryTreeNode(7);
        BinaryTreeNode pNode6 = new BinaryTreeNode(6);
        BinaryTreeNode pNode5 = new BinaryTreeNode(5);
        BinaryTreeNode pNode4 = new BinaryTreeNode(4);

        pNode8.connectTreeNodes(null, pNode7);
        pNode7.connectTreeNodes(null, pNode6);
        pNode6.connectTreeNodes(null, pNode5);
        pNode5.connectTreeNodes(null, pNode4);

        Test("Test3",pNode8);
        pNode8 = null;
    }

    // 测试空二叉树：根结点为空指针
    public static void Test4() {
        System.out.println("\n=====Test4 starts:=====");
        BinaryTreeNode pNode = null;

        Test("Test4",pNode);
    }

    // 测试只有一个结点的二叉树
    public static void Test5() {
        System.out.println("=====Test5 starts:=====");
        BinaryTreeNode pNode8 = new BinaryTreeNode(8);

        Test("Test5",pNode8);
        pNode8 = null;
    }

    public static void main(String[] args) {
        Test1();
        Test2();
        Test3();
        Test4();
        Test5();
    }
}

结果输出：

=====Test1 starts:=====

Test1 Begin:

8 6 10 5 7 9 11

=====Test2 starts:=====

Test2 Begin:

8 7 6 5 4

=====Test3 starts:=====

Test3 Begin:

8 7 6 5 4

=====Test4 starts:=====

Test4 Begin:

=====Test5 starts:=====

Test5 Begin:

8